TOMASSO -v- IG MARKETS LTD [2026] WASC 219

[2026] WASC 219 Page 1 JURISDICTION : SUPREME COURT OF WESTERN AUSTRALIA IN CHAMBERS CITATION : TOMASSO -v- IG MARKETS LTD [No 2] [2026] WASC 219 CORAM : HILL J HEARD : 1 DECEMBER 2025 DELIVERED : 4 JUNE 2026 FILE NO/S : COR 103 of 2022 BETWEEN : ADAM ANTHONY TOMASSO Plaintiff AND IG MARKETS LTD Defendant IG MARKETS LTD Plaintiff by counterclaim ADAM ANTHONY TOMASSO Defendant by counterclaim Catchwords: Practice and procedure - Application for leave to amend defence and counterclaim after trial and delivery of reasons for decision - Whether proposed amendment reflects the manner in which the trial was conducted - Whether court should exercise discretion to grant amendment - Relevant case management principles - Turns on own facts -- 1 of 19 -- [2026] WASC 219 Page 2 Legislation: Rules of the Supreme Court 1971 (WA) O 21 r 5(2) Result: Application dismissed Category: B Representation: Counsel: Plaintiff : M J Sims SC & I M O Matthews Defendant : J Garas SC & M Forgacs Plaintiff by counterclaim : J Garas SC & M Forgacs Defendant by counterclaim : M J Sims SC & I M O Matthews Solicitors: Plaintiff : Chew+Matthews Defendant : King & Wood Mallesons Plaintiff by counterclaim : King & Wood Mallesons Defendant by counterclaim : Chew+Matthews Case(s) referred to in decision(s): Genocanna Nominees Pty Ltd v Thirsty Point Pty Ltd [No 2] [2006] FCA 1335 Gunn v Meiners [2022] WASCA 95 Hightime Investments Pty Ltd v Lungan [No 2] [2010] WASC 296 Irani v St George Bank Ltd [2004] VSC 260 Mackenzie v Albany Finance Ltd [2003] WASC 100 (S) Macks v Viscariello [2017] SASCFC 172; (2017) 130 SASR 1 Mirabela Nickel Ltd v Mining Standards International Pty Ltd [2025] WASCA 82 Nationwide News Pty Ltd v Moodie [2003] WASCA 273; (2003) 28 WAR 314 Nyoni v Patterson [2012] WASCA 171 Sino Iron Pty Ltd v Mineralogy Pty Ltd [2014] WASC 406 Tomasso v IG Markets Ltd [2025] WASC 338 -- 2 of 19 -- [2026] WASC 219 HILL J Page 3 HILL J: 1 The trial of these proceedings occurred in March 2024. At the conclusion of the trial, I reserved my decision. On 21 August 2025, I published my reasons for decision.1 To date, no orders have been made to reflect the Primary Reasons because on 21 August 2025, at the request of both parties, the originating process was adjourned until 19 September 2025. 2 Prior to 19 September 2025, the parties filed a minute of consent orders which foreshadowed an application by IG Markets to amend its defence and counterclaim. Orders were then made for the filing and service of this proposed application and to program it through to a hearing on 1 December 2025.2 3 On 3 October 2025, six weeks after publication of the Primary Reasons, IG Markets filed an application for leave to amend its defence and counterclaim. Specifically, IG Markets seeks leave to amend [37] of its counterclaim to add the underlined text: At the time of entering into each of those contracts, IG Markets believed that those contracts were in relation to a stock, share, futures contract, forward or option contract, commodity, precious metal, Exchange Rate, interest rate, debt instrument, stock or other index, digital asset or other investment but not the 'Test FX Up' market referred to in paragraph 39 below, and paragraph 25.2 above, which IG inadvertently made available and visible to its customers on its platform, being the Error. 4 IG Markets submitted that the 'substance' of the counterclaim, which had been addressed by both parties at the trial, was that Mr Tomasso knew or suspected he was trading on a test market that had inadvertently been made available for trading.3 Senior counsel for IG Markets submitted that as the proposed amendment was consistent with the manner in which the trial was conducted by both parties, if leave were granted, there would be no requirement to re-open the hearing. On this basis, IG Markets contended Mr Tomasso would not suffer any irremediable prejudice if the application were granted. This was notwithstanding the candid admission by IG Markets that it says it will be entitled to judgment on its counterclaim if this application is 1 Tomasso v IG Markets Ltd [2025] WASC 338 (Primary Reasons). In these reasons, I have adopted the definitions used in the Primary Reasons. 2 Orders dated 24 September 2025. 3 Defendant's submissions in support of amendment application filed 3 October 2025 (Defendant's submissions) [4]. -- 3 of 19 -- [2026] WASC 219 HILL J Page 4 allowed.4 This is in distinct contrast to the current position, where the Primary Reasons provide for the counterclaim to be dismissed. 5 Mr Tomasso opposed the application, primarily on three grounds.5 First, the proposed amendment would be futile and inconsistent with the Primary Reasons. Second, the manner in which the trial was conducted by both parties did not depart from the pleadings or broaden the issues between them. Third, case management and discretionary factors weigh against the granting of the application. Mr Tomasso drew attention to the significant delay by IG Markets in bringing the application and the absence of any explanation for the delay. Mr Tomasso also submitted that if the application were allowed, it would be necessary for the case to be re-opened to enable further submissions to be made, and for further or amended reasons to be given. 6 For the reasons that follow, it is my view that leave should not be granted to IG Markets to amend its counterclaim and the application should be dismissed. Legal principles 7 Order 21 r 5(2) of the Rules of the Supreme Court 1971 (WA) (Rules) provides that: The Court may at any stage of the proceedings, without determining whether any relevant period of limitation has expired, allow the plaintiff to amend the plaintiff's writ, or any party to amend that party's pleading, on any terms as to costs or otherwise that may be just and in the manner (if any) that the Court may direct. 8 As was accepted by both parties, O 21 r 5(2) of the Rules enables an application for amendment to be made at any time, including after trial and after the delivery of the court's reasons for decision.6 9 In Hightime Investments Pty Ltd v Lungan [No 2], Beech J summarised the considerations the court will have regard to in considering a late application to amend pleadings:7 (a) the effect of an amendment on the court and on other litigants is relevant; 4 ts 507. 5 Plaintiff's submissions in response to amendment application dated 24 October 2025 [4]. 6 See for example Genocanna Nominees Pty Ltd v Thirsty Point Pty Ltd [No 2] [2006] FCA 1335. 7 Hightime Investments Pty Ltd v Lungan [No 2] [2010] WASC 296 [52]. -- 4 of 19 -- [2026] WASC 219 HILL J Page 5 (b) there is no right to amend to introduce an arguable case and it is wrong to say that only in extreme circumstances would a party be shut out from litigating an arguable case; (c) justice requires that parties have a proper opportunity to plead their case, but limits may be placed on repleading when delay and cost are taken into account; (d) a just resolution does not mean that a party will always be permitted to raise any arguable case at any point in the proceedings, on payment of costs, even indemnity costs; (e) the inevitable strains of litigation must be taken into account in weighing the adverse consequences of delay - this applies to natural persons and other litigants; (f) the nature and importance of the amendment to the party amending must be taken into account; (g) attention must be given to the extent of the delay, and the costs associated with it, the prejudice which might reasonably be assumed to follow from it and any prejudice that is shown; (h) the point in the litigation relative to the trial may be an important consideration; (i) where a discretion is sought to be exercised in favour of a party, an explanation will be called for; and (j) the point can be reached where a party has had a sufficient opportunity to put its case. 10 In Sino Iron Pty Ltd v Mineralogy Pty Ltd, Edelman J added to these considerations the provisions of O 1 r 4A, which provides that a goal of the practice and procedure of this court is the elimination of delay, and O 1 r 4B which includes as principles of case management the just determination of litigation, the efficient disposition of the court's business, the efficient use of judicial resources, the timely disposal of business, and proportionality.8 11 The court will rarely grant leave to amend after reasons for decision are published, if the proposed amendments raise legal or factual issues that have not previously been addressed,9 or where the amendments are inconsistent with the published reasons or go beyond the findings in the reasons.10 This is because this course is 'inconsistent 8 Sino Iron Pty Ltd v Mineralogy Pty Ltd [2014] WASC 406 [30] - [32]. 9 Irani v St George Bank Ltd [2004] VSC 260 [24]. 10 Mackenzie v Albany Finance Ltd [2003] WASC 100 (S) [8]. -- 5 of 19 -- [2026] WASC 219 HILL J Page 6 with the common law tradition of a trial which is presented orally and where the issues are determined once and for all after argument by the parties'.11 12 The two main functions of pleadings were summarised by the Court of Appeal in Gunn v Meiners in the following terms:12 First, to define the issues for decision so that the court can control the preparation of the case and the conduct of the trial. Second, to ensure a fair trial by putting the other party on notice of the case to be met. In the latter respect, the function of a pleading is to state the case that must be met with 'sufficient clarity'. It follows from the procedural fairness aspect that attends the function of the parties' pleadings that, as a general rule, relief is confined to that available on the pleadings. Thus it is an error for a trial judge to decide a case relying on reasons or grounds that were not raised on the pleadings or otherwise go beyond the issues joined between the parties at trial. However, as is implicit in what we have just said, a case may be litigated at trial in a manner that is materially different from the issues as defined by the pleadings. The parties may disregard the pleadings - either confining or enlarging the issues - and fight the case on issues chosen at the trial. It is well established that where this occurs the parties cannot return to the pleadings as governing the area of contest (although there should be an appropriate amendment so that the cause of action alleged forms part of the court record). The position is summarised by Mason CJ and Gaudron J in Banque Commerciale SA (En Liqn) v Akhil Holdings Ltd in a passage that should be repeated: [P]leadings serve to ensure the basic requirement of procedural fairness that a party should have the opportunity of meeting the case against him or her and, incidentally, to define the issues for decision. The rule that, in general, relief is confined to that available on the pleadings secures a party's right to this basic requirement of procedural fairness. Accordingly, the circumstances in which a case may be decided on a basis different from that disclosed by the pleadings are limited to those in which the parties have deliberately chosen some different basis for the determination of their respective rights and liabilities. Their Honours go on to explain that, ordinarily, the question whether the parties have chosen some issue different from that disclosed in the pleadings as the basis for the determination of their respective rights 11 Irani v St George Bank Ltd [24(1)]. 12 Gunn v Meiners [2022] WASCA 95 [109] - [113]. -- 6 of 19 -- [2026] WASC 219 HILL J Page 7 and liabilities is to be answered by inference from the way in which the trial was conducted. 13 In general, the common law rule that applies to all causes of action (including matters in the corporations list that have been ordered to proceed by way of pleadings) is that pleadings define the issues to be determined in proceedings and parties are bound by their pleadings.13 14 However, as the Court of Appeal held in Mirabela Nickel Ltd v Mining Standards International Pty Ltd:14 There is … no 'right' whereby a litigant may hold another litigant to a particular pleaded case. The rules contemplate that the court may allow any party to amend its pleadings at any stage of the proceedings on any terms as may be just: Rules of the Supreme Court 1971 (WA) O 21 r 5(2). Where, as here, a litigant has had a full opportunity, of which it availed itself, to answer a case as presented at trial even though that case strictly exceeded the pleaded case, it cannot be said that there is any infringement of the litigant's rights in allowing an amendment so that the pleadings reflect the manner in which the case was conducted at trial. 15 In considering an application for amendment after trial, it is necessary to consider both the requirements of natural justice and the court's objective to finally determine the issues in dispute between the parties. As the Full Court of the Supreme Court of South Australia stated in Macks v Viscariello:15 Obviously, procedural fairness is the dominant consideration when an application to amend is made after the trial has been completed. However, the question of whether an amendment should be allowed is within the discretion of the Primary Judge. Accordingly, the principles relevant to an appeal from the exercise of a judicial discretion apply and an appeal court should recognise the unique advantage that the Primary Judge had in determining whether it is in the interests of justice to permit an amendment to the pleadings. That is especially where the amendment is sought after the reasons have been delivered. At that point, the Primary Judge will have completed the complex analysis involved in judicial decision-making and will be well placed to determine whether it would be unjust to allow an amendment to the pleadings. 13 Nationwide News Pty Ltd v Moodie [2003] WASCA 273; (2003) 28 WAR 314 [3]. 14 Mirabela Nickel Ltd v Mining Standards International Pty Ltd [2025] WASCA 82 [66]. 15 Macks v Viscariello [2017] SASCFC 172; (2017) 130 SASR 1 [112]. -- 7 of 19 -- [2026] WASC 219 HILL J Page 8 16 Finally, leave will not be given to amend a pleading if the amended pleading is in a form that ought be struck out.16 Materials relied on in support of the application 17 IG Markets did not file any evidence in support of its application. It relied on the following documents: (a) the Primary Reasons; (b) the existing pleadings; (c) the witness outline of Mr Tomasso filed 23 June 2023; (d) Mr Tomasso's opening submissions filed 26 February 2024; (e) IG Market's opening submissions filed 6 March 2024; (f) Mr Tomasso's written closing submissions filed 22 March 2024; (g) IG Market's written closing submissions filed 22 March 2024; and (h) the transcript from the trial. 18 Senior counsel for Mr Tomasso submitted IG Markets' failure to file any evidence explaining their delay in bringing the application was fatal to its success. 19 I do not accept this submission. The basis for IG Markets' application is that the pleadings should be amended to reflect how the case was run at trial. I accept IG Markets' submission that in assessing this contention, the documents that are primarily relevant are the pleadings, the submissions of the parties at trial, and the transcript. If IG Markets does not succeed in establishing this contention, the application must fail. Should the defendant have leave to amend its defence and counterclaim? 20 The relevant starting point is the pleadings filed by both parties, which are summarised at [62] - [79] of the Primary Reasons. 21 As noted in this summary, a distinction was drawn between the way the mistake was pleaded in IG Markets' defence and its pleading in the counterclaim. In its defence, and in the event the Transactions were 16 Nyoni v Patterson [2012] WASCA 171 [38]. -- 8 of 19 -- [2026] WASC 219 HILL J Page 9 held to be 'Transactions' within the meaning of the Agreement, in support of the contention that it validly applied and relied on Term 11 to void the Transactions, IG Markets pleaded at [25.2] that: the Transactions were based on an error which IG Markets reasonably believed to be obvious or palpable, namely, that the 'Test FX Up' trading screen was a test market which had inadvertently been made visible to IG Markets' customers (Error). 22 Relevantly, this paragraph pleaded three matters. First, it identified the Error. Second, it contended that IG Markets reasonably believed this Error to be obvious or palpable. Third, it contended the Transactions were based on the Error. 23 Given this analysis, I accept that Mr Tomasso could not give relevant evidence on any of these matters. 24 In its counterclaim, IG Markets expressly stated that [33] - [44] of its counterclaim were pleaded as an alternative to [15.2] (which addressed whether the Transactions were in relation to an Instrument, constituted a 'Transaction' as defined in the Agreement, or created rights between Mr Tomasso and IG Markets) and [25.2] of its defence. 25 In [38] of its counterclaim, in addressing its claim of unilateral mistake, IG Markets pleaded the serious mistake comprised the matters set out in [37] of the counterclaim, namely that: At the time of entering into the First Purported Transactions and the Second Purported Transactions, IG Markets believed that those contracts were in relation to a stock, share, futures contract, forward or option contract, commodity, precious metal, Exchange Rate, interest rate, debt instrument, stock or other index, digital asset or other investment. 26 Senior counsel for IG Markets submitted the defence focussed on the proper construction of the Agreement, which was required to be determined objectively, whereas the counterclaim raised factual matters concerning the Test FX UP market. On the basis of the express pleading that the counterclaim was an alternative to [25.2], IG Markets submitted the factual matters pleaded in [25.2] informed the counterclaim. 27 For the following reasons, I do not accept these submissions. 28 First, IG Markets' defence did not focus solely on the proper construction of the Agreement but also addressed the factual basis on -- 9 of 19 -- [2026] WASC 219 HILL J Page 10 which it contended it had relied on Term 11 of the Agreement. It is clear from the terms and position of [25.2] within the defence that this paragraph addresses factual matters and not the proper construction of the Agreement. IG Markets' contentions on the proper construction of the Agreement and whether Term 11 was an unfair contract term are set out at [4] - [19] of its defence. Paragraph 25.2 responds to the factual allegations about the Transactions in the statement of claim and sets out the basis on which it is said that IG Markets was entitled to exercise its rights under Term 11 of the Agreement. This was in issue at trial until immediately prior to the closing submissions.17 29 Second, the counterclaim is pleaded as 'an alternative' to [15.2] and [25.2] of the defence. Given this, I do not accept that, as pleaded, the matters in [25.2] informed the counterclaim. The use of the word 'alternative' makes it clear that the counterclaim contained a separate and distinct plea to that contained in [25.2] and required the court to consider IG Markets' position if the Transactions were held to be 'Transactions' within the meaning of the Agreement and did not accept IG Markets had validly exercised its rights under Term 11 to void the Transactions from the outset. 30 Third, the word 'Error', which is a defined term in the defence, does not appear anywhere in the counterclaim. This supports a conclusion that IG Markets did not intend the Error to form part of its counterclaim. 31 At [32] - [36] of the counterclaim, IG Markets set out the provisions of the Agreement which were relevant to its counterclaim. Relevantly, IG Markets pleaded that each contract (or Transaction) was formed by Mr Tomasso offering to open or close the relevant transaction in respect of Test FX UP at the level or amount quoted by IG Markets, and this offer being received and accepted by IG Markets. Each of these Transactions was pleaded to be a separate contract which IG Markets believed to be a 'transaction' as defined in the Agreement. 32 The unamended [37] of the counterclaim then contended that at the time of entry into each contract (or Transaction), IG Markets believed the contracts to be a 'Transaction' as defined in the Agreement. In [38], this is said to be the reason that IG Markets was operating under a serious mistake. 17 Defendant's closing submissions filed 22 March 2024 (Defendant's closing submissions) [5]. -- 10 of 19 -- [2026] WASC 219 HILL J Page 11 33 At [39] of its counterclaim, IG Markets pleaded that Mr Tomasso was aware of the following matters, namely: (a) the 'Test FX UP' market was labelled as a test market; (b) the prices on this market moved up linearly before declining linearly at midnight London time; and (c) prices increased from approximately 8 points to approximately 863,398 every day. 34 At [40] and [41] of the counterclaim, it is these three matters which are said to give rise to Mr Tomasso being aware or suspecting that circumstances existed which indicated IG Markets was entering into the Transactions under a serious mistake in relation to a fundamental term or subject matter. 35 Nowhere in the defence does IG Markets specifically identify what the serious mistake was or identify what fundamental term or subject matter the mistake concerned. On its face, the matters in [39] and the allegations in [40] and [41] focussed on Mr Tomasso's knowledge of certain features of the Test FX UP market rather than whether Mr Tomasso was aware the Test FX UP market had been made available for trading by mistake (which is the Error pleaded in [25.2]). 36 IG Markets also contended that, on the basis of a common mistake, each of the Transactions was void as each purported to be a CFD in the value or price of an underlying instrument and currency, when these differences did not exist. 37 In his defence to [39] of the counterclaim, Mr Tomasso admitted he knew the market was labelled 'Test FX UP', denied he knew it was in fact a test market, and then pleaded (in [20(c)]) that: from the time that the plaintiff's Account was opened, and when he entered into the First Transactions and the Second Transactions, IG Markets had many markets available on its Platform with many different and varying names, and that the presence of the word 'Test' in the name of the Market was not in all the circumstances sufficient to convey to the plaintiff, or a reasonable person in the plaintiff's position, that IG Markets had inadvertently made the Market available and visible to its customers on its Platform[.] 38 A similar defence was pleaded by Mr Tomasso in defence to the claim of common mistake (at [24A(c)] of the defence to the counterclaim), namely that: -- 11 of 19 -- [2026] WASC 219 HILL J Page 12 if (which is denied), he and IG Markets made any common mistake as to the existence of the subject matter of the Agreement, the First Transactions or the Second Transactions, such common mistake was induced by the carelessness or negligence of IG Markets in making the Market visible to IG Markets' customers (including the plaintiff) on the Platform[.] 39 I accept IG Markets' submission that Mr Tomasso's pleaded response to its claims of unilateral and common mistake was not limited to the features of the Test FX UP market but also raised whether the reference to 'test market' in Test FX UP was sufficient to indicate this market had been made available to IG Markets' clients by mistake, which is the mistake defined in [25.2] of the defence as the Error. 40 Both parties opened their case in a manner consistent with their pleadings. 41 In Mr Tomasso's written opening submissions, [25.2] of the defence was said to be relevant to the question of the application of Term 11, in the event it was held not to be void. In relation to the defence of unilateral mistake, after noting the elements IG Markets was required to establish (summarised at [287(b)] to [287(d)] of the Primary Reasons) Mr Tomasso submitted in relation to the first element that 'IG [Markets] will not be able to establish that it was operating under the pleaded serious mistake' because the Transactions were in relation to an 'investment'.18 In relation to the second and third elements of unilateral mistake, he submitted that 'the evidence will establish that Mr Tomasso did not have any doubts as to the legitimacy of the Markets or his trading on them'.19 42 Consistent with these submissions, in his oral opening, senior counsel for Mr Tomasso submitted that 'Mr Tomasso did not know the Test FX Up market had been made available to trade by IG in error' and that he believed it was a legitimate market.20 Senior counsel for Mr Tomasso made it clear there was no dispute the Test FX UP market had been made available for trading (referring to [25(2)] of the defence), but denied IG Markets made any error as to the nature or operation of the Test FX Up market or believed the Transactions were 'transactions' within the meaning of the Agreement. 18 Plaintiff's opening submissions filed 26 February 2024 (Plaintiff's opening submissions) [132]. 19 Plaintiff's opening submissions [138]. 20 ts 59 - 60. -- 12 of 19 -- [2026] WASC 219 HILL J Page 13 43 At the commencement of the opening submissions by IG Markets, senior counsel for Mr Tomasso (following an exchange between the court and senior counsel for IG Markets) clarified his client's position in the following terms:21 We accept an error took place. So the objective existence of an error is not in dispute. The error was making the market live when it ought not to have been made live. We don't accept – and it's for Mr Garas – Mr Garas' client to prove, through its witnesses, that a belief formed that the error was obvious or palpable was necessarily a reasonable belief. The point I made about the nature of the error and the importance of the nature of the error is perhaps – and the fact that IG knew what it was posting is not related to term 11 arguments. It's related to the errors which are said to underpin the unilateral mistake and res extincta counter-claims, and those errors are pleaded in a different way, and so I don't accept that IG made the errors it pleads in its unilateral mistake and/or res extincta claim, but I accept the – and Mr Tomasso accepts the objective fact of an error, being the posting of the market inadvertently. 44 In response, senior counsel for IG Markets simply noted this was of assistance. 45 The reference to the objective factual error is the matter referred to in IG Markets' written opening submissions without reference to its pleadings.22 In its written opening submissions on unilateral mistake, IG Markets did not specifically identify the mistake it relied on. It simply contended that the primary factual issue was 'Mr Tomasso's knowledge or suspicion that IG [Markets] was acting under a mistake at the time it entered into the relevant transactions (by its automated systems accepting Mr Tomasso's offers)'. IG Markets identified the legal issue in relation to unilateral mistake as being whether each transaction was a separate contract.23 46 In IG Markets' opening submissions, it stated that [25.2] was relevant to the issue as to whether Term 11(1) applied on the facts to void the relevant transactions,24 and was not relied upon in support of its counterclaim.25 21 ts 107. 22 Defendant's opening submissions dated 6 March 2024 (Defendant's opening submissions) [1], [13]. 23 Defendant's opening submissions [198], [199]. 24 Defendant's opening submissions [35], fn 22. 25 See Defendant's opening submissions [39], fn 25. -- 13 of 19 -- [2026] WASC 219 HILL J Page 14 47 In his oral opening submissions, senior counsel for IG Markets did not add to the written submissions on unilateral mistake and reiterated this would depend on Mr Tomasso's evidence.26 48 IG Markets relied on both Mr Tomasso's witness outline and his cross-examination which addressed Mr Tomasso's knowledge or suspicion that Test FX UP was not a 'legitimate' market or that it was not intended to be available for trading.27 IG Markets emphasised that a witness outline is required to address only the matters in issue between the parties,28 and drew attention to the fact that no objection was taken by Mr Tomasso's senior counsel to this line of questions.29 49 At trial, both parties accepted that Mr Tomasso's evidence was only relevant to the counterclaim.30 Given this, senior counsel for IG Markets submitted his evidence could only be relevant to the question of unilateral mistake. 50 While I accept that Mr Tomasso was cross-examined about whether he believed IG Markets had made an error in making the Test FX UP market available for trading,31 he was also asked numerous questions about whether he believed the Transactions were a binary option or a binary option CFD, the relevant features of each of these options in comparison to the Transactions, and whether he knew the Test FX Up market only moved in one direction.32 Much of Mr Tomasso's evidence relied upon by IG Markets concerned his cross- examination on the features of the Test FX UP market, which was put in issue by [39] of its defence and counterclaim, and whether the Test FX UP market was a 'real market',33 which was relevant to the way in which IG Markets pleaded its counterclaim. 51 In IG Markets' written closing submissions, IG Markets submitted that, in relation to Mr Tomasso's evidence, that: 34 he was not aware or never suspected that Test FX Up was not a real market, is rife with inconsistencies and, assessed in the totality of the circumstances – including his trades and attempts to execute trades in 26 ts 136 - 137. 27 Witness Outline of Adam Anthony Tomasso filed 23 June 2023 [12], [20]; ts 175, 179, 180, 186 - 189, 192, 193, 195 - 197. 28 Consolidated Practice Direction 4.5.1 [7]. 29 Defendant's submissions [54]. 30 Plaintiff's closing submissions filed 22 March 2024 (Plaintiff's closing submissions) [36]. 31 See for example ts 187, 193, 196, 197. 32 ts 177. 33 See for example ts 175, 179, 188 - 189, 196. 34 Defendant's closing submissions [12]. -- 14 of 19 -- [2026] WASC 219 HILL J Page 15 the 35-minute window – is utterly implausible. He should not be believed; and it should be inferred that he was aware or at least suspected a mistake by IG, and embarked on a course of action to take advantage of the situation. 52 In the Primary Reasons,35 in addressing the question of unilateral mistake, I identified the statement by IG Markets in their closing submissions (at [19]) that Test FX UP (as well as Test FX DOWN) were inadvertently displayed and made available on the live platform due to an internal error as a submission. On reflection, given where this statement appears in the submissions, it is more accurate to describe this statement as forming part of the background facts rather than as a submission. 53 In their written closing submissions, IG Markets addressed the question as to whether the Transactions should be vitiated for unilateral mistake at some length at [293] - [348]. IG Markets identified the serious mistake as being:36 the contents of the contracts in relation to a fundamental term or the subject matter of those contracts. That was because it was unaware, when the Test FX UP trades were automatically accepted, that test markets had become available to clients on its platform. It thus believed that the contracts, like all other contracts that were being traded through its platform, were in relation to an Instrument (as defined in the Agreement). 54 That is, while IG Markets identified the error as the test markets becoming available for trading, the mistake was said to be its belief that the contracts were in relation to an Instrument. This submission is consistent with IG Markets' pleading as summarised above. 55 In addressing the IG Markets' counterclaim, Mr Tomasso's written closing submissions referred to the pleaded serious mistake and submitted IG Markets had not proved this element as the Transactions were in relation to an 'investment' and that IG Markets never laboured under any mistake as to what the Test FX UP market was.37 56 Importantly, as was quite properly accepted by senior counsel for IG Markets on this application,38 at no stage during the trial did IG Markets contend that Mr Tomasso had misunderstood its 35 Primary Reasons [304]. 36 Defendant's closing submissions [303]. 37 Plaintiff's closing submissions [274]. 38 ts 559. -- 15 of 19 -- [2026] WASC 219 HILL J Page 16 counterclaim or that the error in [25.2] underpinned its counterclaim in relation to unilateral mistake. 57 On this application, senior counsel for IG Markets submitted that the proposition put against them at trial was that IG Markets was not mistaken about how the test market was generated and that this is why their counterclaim failed.39 I do not accept this submission. It ignores (or at least minimises) the submissions by both parties as to whether Test FX UP was a 'real market' and whether, as a consequence, the Transactions were a 'transaction' as defined in the Agreement. 58 In my view, at trial, both the pleadings and the submissions of the parties distinguished between IG Markets' error in making the market referred to as Test FX UP available for trading (which was not in dispute) and what was said to be the mistake concerning a term or subject matter of the contract. 59 In its submissions in support of this application, IG Markets did not clearly or consistently identify what it contended the relevant mistake was concerning the term or subject matter of the contract. Initially, IG Markets said the Error (as defined in [25.2]) 'lay at the heart of the alleged mistaken belief' as it believed the Transactions were in relation to a 'real instrument'40 or a 'real or legitimate market'.41 Subsequently,42 IG Markets conflated the Error and the mistake. It submitted that the Error was the mistake that produced IG Markets' mistake, such that it led to a mistake as to the subject matter of the contracts and affected the plaintiff's conscience in equity. In oral submissions, senior counsel for IG Markets explained this submission in terms that its claim was that the Transactions should be vitiated because IG Markets never intended to activate the Test FX UP market which is the mistake as to the content of each of the Transactions.43 60 IG Markets' initial submission is, in my view, consistent with the existing pleadings. This submission was addressed and rejected in the Primary Reasons at [306]. For the reasons set out at [259] - [275] of the Primary Reasons, I concluded that each of the Transactions was in relation to an Instrument. 39 ts 493 - 494. 40 Defendant's submissions [28]. 41 Defendant's submissions in reply on amendment application filed 7 November 2025 [3]. 42 Defendant's submissions [29]. 43 ts 514 - 515. -- 16 of 19 -- [2026] WASC 219 HILL J Page 17 61 In relation to the subsequent submission, it is important to emphasise that the Transactions in question were formed by computerised trading systems and that it was IG Markets that accepted the offer of Mr Tomasso and not Mr Tomasso accepting IG Markets' offer. That is, once an offer was made by Mr Tomasso, based on a quote produced by IG Markets' computerised trading system, it was accepted automatically by IG Markets' computerised trading system without human intervention.44 This is how IG Markets designed its systems and how they were intended to work. 62 On the application, IG Markets did not identify how the Error relates to or concerned a fundamental term or subject matter of the contract or explain how the proposed amended pleading sets this out. 63 In this case, the mistake complained of by IG Markets appears to be its assumption that its test markets were not available for trading on its Platform and that, on this basis, it assumed the Transactions did not relate to its test markets. In my view, this is not a mistake about the terms of the Contract; it is a mistake about a fact or assumption on which its algorithms accepted the offer by Mr Tomasso and entered into the Transactions. Unless this fact or assumption formed part of the terms of each of these separate contracts, each of these Transactions remained binding on IG Markets. The proposed amended pleading does not address these matters. 64 Having reviewed each of the matters relied upon by IG Markets in support of its application, I do not accept that the parties conducted themselves at trial on the basis that: (a) the Error was the relevant mistake as to a fundamental term or subject matter of the contract; and (b) if it were established Mr Tomasso was aware or suspected that the Test FX UP market had been made available for trading by mistake, this would be sufficient for IG Markets to succeed on its counterclaim. 65 Given these conclusions, I do not accept that IG Markets should have leave to amend its defence and counterclaim. 66 In any event, even if I had been satisfied that the proposed amendment reflected the manner in which the case was run at trial, for 44 See Primary Reasons [123] - [124]. -- 17 of 19 -- [2026] WASC 219 HILL J Page 18 four primary reasons, I would not have exercised my discretion to allow the amendment at this late stage. 67 First, in my view, if the amendment were allowed, it would be necessary, at a minimum, to allow the parties to make further submissions in relation to the counterclaim and for supplementary reasons to be delivered. In my view, the parties would need to be given the opportunity to specifically address whether the Error concerned a fundamental term or the subject matter of each of the Transactions, particularly given my conclusion that each Transaction was in relation to an Instrument as defined in the Agreement, and the consequent impact on my conclusion on the counterclaim. To allow this to occur would be inconsistent with the efficient use of judicial resources and the timely disposal of this case. 68 Second, in seeking to conflate the Error and the mistake, the proposed amendment is inconsistent with the conclusion in the Primary Reasons that the Transactions are in relation to an Instrument, as that term is defined in the Agreement. The finding that at the time each of the Transactions was entered into, the relevant employees of IG Markets were unaware the Test Markets had become available for trading does not, in my view, assist IG Markets on its present application. This is because IG Markets' belief at the time of entry into each of the Transactions, that each Transaction related to an Investment was correct. As stated in the Primary Reasons, by making the Test Markets available for trading, the Test Markets were an 'investment'. 69 Third, no explanation has been proffered by IG Markets for its delay in bringing this application. In my view, IG Markets has had a sufficient opportunity to address Mr Tomasso's claim and prosecute its counterclaim, and it should not be entitled to now run the claim set out in its proposed amendment. 70 Fourth, and in any event, in failing to identify the mistake or how this relates to or concerns a fundamental term or subject matter of the contract, it is my view that the proposed amended pleading is in a form that ought be struck out. Given this, I do not consider that leave should be granted to amend the pleading in this form. Conclusion and orders 71 For these reasons, IG Markets' application to amend its counterclaim will be dismissed. My preliminary view is that the costs of the application should follow the event, namely that IG Markets -- 18 of 19 -- [2026] WASC 219 HILL J Page 19 should pay the costs of the application. However, before making any formal orders, I will hear from the parties. I certify that the preceding paragraph(s) comprise the reasons for decision of the Supreme Court of Western Australia. KS Associate to the Hon Justice Hill 4 JUNE 2026 -- 19 of 19 --