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Intervening in EPO opposition proceedings


The deadline of 9-months from grant for opposing a European patent is one of the few absolute deadlines set by the European Patent Office but it does not represent the last chance to get involved in EP opposition proceedings.  Even if you have missed this 9-month term there is still, under very specific circumstances, the opportunity to “intervene” in pending opposition (or opposition-appeal) proceedings. 

The right to intervene is governed by Article 105 EPC which states that any third party may intervene in opposition proceedings after the opposition period has expired, if the third party proves that:  

a) proceedings for infringement of the same patent have been instituted against him, or 
b) following a request of the proprietor of the patent to cease alleged infringement, the third party has instituted proceedings for a ruling that he is not infringing the patent. 

In recent years there has been much debate regarding what constitutes “proceedings for infringement” but as this is not the focus of this particular article, it is suffice to say that if a patentee uses the national part of their EP patent to limit the commercial activities of a third party, they run the risk of an intervention in the event there are already on-going EP opposition proceedings relating to that patent.  So if, as a patentee, you do not want additional parties being involved in an opposition against your patent, do not enforce it until the opposition proceedings have been finally resolved.  In the event you are considering suing an existing opponent you should also make sure that you sue the same legal entity that has opposed you.  If you do not, then the sued entity can also intervene and potentially benefit from some of the advantages discussed below.

The mechanism for intervening in opposition proceedings is straightforward; the intervener has to file their grounds for opposition (together with the corresponding fee) within 3-months of the proceedings being instituted against them.  This should also be accompanied by evidence of when and where the proceedings have been instituted – e.g. the court papers showing the date upon which the action was filed.  When calculating the 3-month term we would advise erring on the side of caution as the date on which proceedings are deemed to have been instituted may vary from country to country.  Where possible, do not wait until the end of the 3-month term.  If deemed admissible, the intervention shall be treated as an opposition.

So why file an intervention?

On the face of it, there appears to be no downside to intervening in opposition proceedings.  The most obvious advantage is that you get a chance to be involved in revoking the EP patent centrally, for relatively little cost.  Another important aspect if you happen to be sued in Germany, is that an intervention is the only way you can challenge the validity of the patent as long as the opposition proceedings are pending; parallel nullity actions in Germany are not available.  Similarly, in Austria and Hungary, although national revocation actions may be filed in parallel they will be suspended for the duration of the EPO opposition proceedings.

However, despite these advantages, there are more nuanced aspects that a potential intervener should consider before diving blindly into an intervention. 


Subject to the 3-month deadline discussed above, an intervention can be filed at any point during the pending opposition proceedings and when it is filed, it is treated as a fully-fledged opposition.  This can be effective if you are intervening 12 to 18 months after grant of the patent, when the proceedings are fresh and you have a real chance to influence them, but it may be of less value later in the proceedings when opinions are set, particularly if the case is already under appeal. 

That said, intervening at the appeal stage has the notable upside that new prior art and arguments can be introduced at a point in the proceedings when the Rules of Procedure of the Boards of Appeal (RPBA) would have otherwise prevented opponents from introducing them into the proceedings (or at least made it very difficult).  However, the same intervention also gives the patentee an excuse to introduce new arguments and evidence under the pre-text that they are responding to the “new” opposition.  In such a situation, the intervener should think carefully about what their intervention is adding to the pending proceedings.  If filing an intervention late in the proceedings simply gives the patentee an opportunity to file new arguments, without significantly improving on the arguments of the existing opponents, is it really worth it?

Another consideration with an intervention is that, as a party to the opposition proceedings, an intervener may request accelerated proceedings to get a faster decision on the validity of the patent.  However, if the intervention introduces any new arguments and evidence, it could be used by the patentee to request additional time to deal with these arguments.  Experience has taught us that the EPO’s sensitivity towards being accused of not giving parties their right to be heard can lend itself to extensions being allowed for the most spurious of reasons.

How will my intervention improve the case?

Simply being a party to the opposition proceedings may be reason enough to file an intervention.  Indeed, as long as you are not a party to the proceedings there is always the risk that the opponents will settle leaving you with no option but to file national revocation actions.  Nonetheless, the intervener should always ask themselves “what am I bringing to the proceedings?” 

Clearly having the chance to introduce a critical piece of prior art, particularly during appeal proceedings when it would otherwise be difficult to do so, is a huge upside that could make or break a case.  However, for the reasons discussed above, simply repeating arguments already on file may just give the patentee the chance to file new evidence and arguments or even delay the proceedings, without offering any upside to the opposition as a whole.

The number of existing opponents may also influence the value of an intervention.  With just one or two opponents an intervener has a realistic chance of getting their point across and being able to influence the proceedings.  Conversely, joining as the tenth opponent may significantly reduce the impact of the intervention (although being the last to speak in the oral proceedings can carry a certain advantage).

Final thoughts

In conclusion, when a third party gets to file an intervention is completely out of their hands but whether they file it and what they want to achieve from it, is not.  It will be rare that intervening in opposition proceedings will not make sense but that does not mean the potential consequences should not be considered.  At the same time, a patentee should think twice about suing in Europe if opposition proceedings involving the patent in question are still pending (it should go without saying that suing before the 9-month opposition window is closed should be avoided if at all possible). 

In recent times our opposition team has been involved in a number of proceedings involving interventions, acting for both interveners and the patentee.  Despite the significant impact they can have on litigation proceedings, the need for a party to have been sued means that interventions are not particularly common so if you foresee an intervention as either a risk to, or option for, your litigation strategy we would be happy to advise you on your best options. 

This article is for general information only. Its content is not a statement of the law on any subject and does not constitute advice. Please contact Reddie & Grose LLP for advice before taking any action in reliance on it.

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