Held, appeal dismissed. The reason for the introduction of rule 52 of the Employment Tribunals Rules of Procedure 2013 was to avoid the need for respondents to apply to dismiss withdrawn claims, which, prior to its introduction, comprised a significant proportion of all resolutions. Rule 52 addressed the issue of the gap in the Employment Tribunal Rules for finality in litigation or constraints on relitigation, in circumstances where there was no equivalent to the Civil Procedure Rules on discontinuance, which did not result in estoppel, but where a party seeking to make another claim might need the permission of the court to do so. The part of rule 52 in brackets explained to parties the gist of the general common law, namely that of res judicata, including cause of action estoppel. Res judicata encompassed cause of action estoppel, issue estoppel and the principle that a party should be prevented from raising in subsequent proceedings matters which were not, but could and should have been raised in the earlier ones. There would be situations within the scope of res judicata, that did not fall within rule 52, that raised the same, or substantially the same complaint. Moreover, where a judge or tribunal had dismissed a claim after considering its merits (not on withdrawal of the claim, or part of it) the full scope of res judicata was open to a later judge or tribunal to consider, in deciding whether a claim was vexatious or had no reasonable prospect of success (rule 37(1)(a)). It followed that rule 52 applied in circumstances which were far narrower than a tribunal’s general powers to consider and apply res judicata. However, regardless of the application of rule 52, the judge’s conclusion on issue estoppel was not sufficiently explained. The need for a more detailed analysis of issue estoppel was particularly important, given its potentially draconian effects. Issue estoppel could still apply even where a judgment was reached without consideration of a claim on its merits. However, before concluding that issue estoppel applied, a court or tribunal had to be satisfied as to whether the effect of a judgment decided that a particular condition had, or had not, been met. It remained important to identify, through analysis of legal submissions, the actual ground on which the existence of a claim was previously rejected, which the judge in the present case had not done. Accordingly, the judge erred in concluding that the effect of rule 52 was to give rise to estoppel on the facts of the case; and her general analysis of issue estoppel was not sufficiently explained. However, she had carefully considered whether the 2021 claims were an abuse of process. She did not err in that analysis or in relation to the allegation that the judge’s interpretation of the COT3 was incompatible with section 43J(1) of the Employment Rights Act 1996, as it would otherwise retrospectively preclude the claimant from relying on having made protected disclosures previously. Nor did she fail to consider arguments about whether the claimant was no longer bound by the terms of the COT3. Accordingly, in the circumstances, the judge’s error concerning rule 52 was not such that her decision to strike out the 2021 claims was unsafe and should be set aside (paras 42, 43, 44, 52, 54, 82).