Period of limitations in follow-on competition cases: when does a 'decision' become final?

A series of private competition law cases in the UK has demonstrated that there are significant procedural issues that need resolving before private enforcement can flourish in the way that the European Commission and the UK Government are currently encouraging. One of these issues is the calculation of the period of limitations in a follow-on case where there are multiple infringers some of whom appeal the infringement decision of the competition authority and some of whom do not. A closely related issue is that of when the underlying infringement decision of the competition authority becomes final and consequently binding on a national court deciding a follow-on case. This has been a recurring problem in the UK in the context of follow-on actions before the Competition Appeal Tribunal (CAT) culminating in the Deutsche Bahn decision of the Supreme Court. This article shows that this seemingly simple issue of establishing when a decision becomes final and the calculation of the period of limitations is in fact loaded with serious implications going well beyond a procedural, timing point. Although the issue is pertinent to all types of infringements of competition law with multiple infringers, it has particular implications for leniency recipients in cartel cases and therefore, for the overall relationship between private and public enforcement of competition law. This article demonstrates how suboptimal the current legal situation is and what the overall preferable solution is for establishing when an infringement decision becomes final and the period of limitations in follow-on cases based on infringement decisions in the presence of multiple infringers under UK and EU law.