The European patent system has undergone rapid transformation since the Unified Patent Court (UPC) opened for business two years ago. The UPC provides a new forum for challenging the validity of European patents, with UPC revocation proceedings now frequently running in parallel with opposition proceedings before the European Patent Office (EPO). With both bodies competent to issue binding decisions on the validity of the same European patent, understanding the procedural interplay between the EPO oppositions and UPC litigation is essential for businesses with European patents or those monitoring competitors’ rights.

Both the EPO and the UPC recognise the importance of legal certainty, procedural efficiency and promoting harmonisation across the European patent system. In this context, the EPO will accelerate opposition proceedings if informed of parallel infringement or revocation proceedings before the UPC or a national court of a contracting state. The UPC aims to hold the oral hearing within one year and the court has discretion to stay revocation proceedings where a parallel EPO opposition is pending, but usually only where the EPO decision is expected within a short timeframe.

These procedural developments have significant implications for European litigation strategy. Parties must carefully consider the timing of EPO oppositions and UPC actions, taking into account how EPO acceleration and the UPC’s discretion to stay proceedings may interact. Parties should also bear in mind that a coherent and coordinated approach with aligned arguments and evidence is essential in parallel proceedings for maintaining credibility, managing risk and maximising prospects for success.

Why the EPO accelerates oppositions

Opposition proceedings before the EPO are a central tool for challenging the validity of European patents. Historically, however, these proceedings could take many years to conclude – creating a significant lag between patent grant and legal certainty, and complicating commercial decision-making, investment and litigation planning.

The EPO’s mechanism for accelerating oppositions helps to address these concerns. A key motivation is the need to keep pace with the broader European patent enforcement framework, especially now that the UPC is in full force and with its stated aim of speed along with high quality. Mismatched timing between EPO oppositions and UPC litigation risks conflicting outcomes and wasted resources – inefficiencies that both the EPO and the UPC are keen to avoid.

The acceleration of oppositions can be significant. If the EPO is notified of parallel proceedings during the nine-month opposition period, then a decision is expected approximately eight months after the end of the opposition period – much faster than the usual 18-24-month opposition duration.

UPC - EPO interplay: practical implications for parties

The EPO will accelerate opposition proceedings if it becomes aware of parallel UPC or national court proceedings relating to the same patent. This may occur even without a specific request by the parties involved. In particular, the EPO operates an internal monitoring system for parallel and national proceedings and can accelerate oppositions on its own initiative. It may therefore not be possible to prevent a parallel EPO opposition from being accelerated, and this should be factored into the parties’ overall litigation strategy.

Only the first instance opposition procedure has this guaranteed acceleration mechanism, although appeals can still be accelerated at the discretion of the Board of Appeal upon reasoned request by a party or the UPC/court of a contracting state (as per RPBA Art. 10(3),(4)). EPO oppositions frequently reach the appeal stage, and so this is another factor which could come into play when considering how parallel proceedings may interact, especially if the EPO Boards of Appeal reach a different conclusion to the EPO Opposition Division, but the UPC have decided on infringement and/or validity in the interim.

Another factor for parties to consider is the UPC’s discretion to stay proceedings where a parallel EPO opposition is ongoing. Unlike the EPO opposition acceleration, UPC stays are not guaranteed – they are more likely when an EPO decision is imminent, and very unlikely when the opposition is at an early or uncertain stage. As such, if a UPC action is filed during the early stages of an EPO opposition, or even on the same day, it is likely that the EPO opposition will be accelerated and the UPC will proceed without a stay. This increases the risk of diverging outcomes. In contrast, a UPC action filed later during a parallel EPO opposition may encourage the UPC to wait for the EPO’s findings. Patent proprietors with a positive preliminary opinion in an EPO opposition could tactically use this to their advantage, and may support a stay of parallel UPC proceedings pending the outcome of the opposition.

Accelerated EPO oppositions mean even tighter deadlines for both parties, alongside the pressure of running two parallel proceedings. This could be used to benefit an opponent, applying pressure on the patentee to quickly defend the patent in two venues. For this reason, there could be tactical advantages for an opponent to file an EPO opposition and UPC revocation action at similar times, as the UPC would be unlikely to stay the proceedings in those circumstances.

Another factor for parties to consider is that the relative timings of EPO oppositions and UPC actions can directly impact settlement dynamics. In particular, an early EPO decision can shift leverage in settlement or licensing discussions in relation to the UPC action.

Finally, a key point for all parties to keep in mind for parallel proceedings is the need for consistency. Arguments used during EPO oppositions should align with those raised before the UPC. Inconsistent positions can damage credibility, weaken the case or result in conflicting decisions. Coordination management across the parallel proceedings is critical.

Timing is a strategic tool

The EPO’s acceleration of oppositions in parallel proceedings, combined with the UPC’s emergence as a leading European litigation venue, signals a new era of procedural complexity in European patent law. It is important for businesses to adapt by developing flexible, forum-aware strategies that anticipate how the timing of decisions in one proceeding may affect outcomes in another. In today’s European patent landscape, successful litigation strategy may require not only a strong case, but also a well-timed one.

Lucy Coe is a partner and patent attorney at European IP firm Mewburn Ellis.