In October 2015, Unite received a complaint from a female member, alleging that the Respondent had slapped her bottom. The first disciplinary proceedings were brought by Unite under rule 27.1.7 of Unite's rulebook and Unite found that the alleged action of the Respondent had occurred and amounted to misconduct. The matter in due course came before the ACO. His decision was that there was no misconduct under rule 27.1.7, because the incident did not occur in the workplace; and that Unite had not relied on any other rules in its rulebook. The ACO declared that Unite's first disciplinary proceedings and the penalties imposed were "null and void and of no effect". Unite brought a second set of disciplinary proceedings against the Respondent on 28 November 2017. These proceedings concerned the same factual allegation, but were brought under rules 27.1.1, 27.1.4 and 27.1.5 of the Unite rulebook. It was determined that the Respondent was in breach of rules 27.1.1, 27.1.4 and 27.1.5. The sanction imposed was that the Respondent was barred from holding office in Unite. After a complaint to the CO by the Respondent, the CO ruled that the doctrine of res judicata does not apply to decisions made under Unite's disciplinary procedures. The CO held that the relationship between Unite and its members is comparable to that between an employer and an employee. The Respondent appealed to the EAT. The EAT ruled that the ACO's decision itself was neither null nor void nor of no effect. The effect of his decision was that the Respondent was not in breach of rule 27.1.7 and that the Union had not relied on any other rules in its rulebook. The Union was estopped by that decision from bringing further disciplinary proceedings alleging that the Respondent had slapped the complainant's bottom and was thereby in breach of rule 27.1.7. Unite appealed to the Court of Appeal.

The Court of Appeal allowed the appeal. The essential question for the court to decide was whether the doctrine of res judicata applies to the disciplinary proceedings of a trade union. Citing the judgment from Elias LJ in Christou v London Borough of Haringey [2013] EWCA Civ 178; [2014] QB 131, the distinction which emerges is between a body which is independent of the parties and is invested by law with the power to determine an issue which establishes the existence of a legal right; and other bodies, which are not. The court concluded that in the present context there was no independent body invested by law with jurisdiction to determine the legal rights of the parties. The doctrine of res judicata does not apply to the disciplinary proceedings of a trade union.