Prior Use ''Pitfalls'' in EPO Oppositions

Prior Use ''Pitfalls'' in EPO Oppositions

This practical update takes a look at how best to use public prior use in an EPO opposition and the potential pitfalls to avoid.   A public prior use attack in opposition may seem like a sure thing, but it’s not as simple as you might expect in practice. 
Here we walk through the issues of:

  1. What evidence is needed for a public prior use attack?

    1. When?

    2. What?

    3. Where?

    4. How?

    5. To whom?

  2. What is the burden of proof for showing a public prior use? and

  3. Are there any different considerations for specific technical fields?



Lack of novelty is a powerful attack in opposition proceedings before the EPO and is usually based on documents with a clearly printed publication date.  But what about the situation where a relevant product has allegedly been sold before the priority date of an EP patent?
It’s unusual for prior use to be raised during examination because searches performed by patent offices are unlikely to find evidence of a prior use. Instead, it is most commonly raised during post-grant opposition proceedings.
Here are some practical tips for defending against a prior use attack or for making one against someone else.
1. What evidence is needed for a public prior use attack?

Since an opponent is unlikely to be able to rely on a single document with a precise publication date disclosing all of the features of the claims, it is usually necessary for the opponent to file several different pieces of evidence to prove the alleged public prior use actually took place.
To succeed with a public prior use attack, an opponent needs to show: (i) when the prior use occurred; (ii) what was made available to the public and (iii) the circumstances of the use, i.e. where, how and by whom (T 1856/11). If any one of these criteria are not met, the attack will fail.  


The opponent needs to provide proof the public prior use occurred before the priority date (or filing date, as the case may be) of the claimed subject-matter.  Surely an invoice showing the product was sold at the right date is enough? Not necessarily – in T1217/01, an invoice was the only document filed by the opponent with such a date, but it did not also disclose the composition of the product that was sold.  In view of changes in product naming and numbering, the opponent could not definitively prove the invoice related to the product in question. 


If the claims relate to a product with a certain property, the opponent must show this property was disclosed in the alleged prior use product, and it also needs to be clear exactly what product was tested by the opponent.  For example, in T 600/90 the opponent argued a sample of a product that had been produced and sold before the priority date of the patent had the desired property.  However, the measurements were made on different samples produced after the filing date of the patent.  The Board held it was not possible to conclude the sale before the priority date constituted a public prior use, despite a statement from the producer of the product that there had been no significant changes to the composition of the product since well before the priority date.  The Board held that even if it were accepted no significant changes were made, there is no evidence the property in question did not vary from batch to batch.  The patent proprietor was therefore given the benefit of the doubt and it was held there was not sufficient evidence to show that the prior use had occurred.


Anywhere ‘public’, although this is not as simple as it sounds.  An alleged public prior use 5 metres inside in a fenced-off area of a shipyard was held not to be ‘public’ in T 245/88 despite the fact the alleged public prior use was visible from the fence.  This was because the public did not have access to the fenced off area and could not determine the claimed features accurately from a distance of 5 metres.
In contrast, while shipyards are normally considered to be restricted areas, in T 2210/12, the installation of machinery on Volkswagen’s private factory premises was held to be a public prior use because Volkswagen as a company counted as part of the public and the machinery’s delivery was not subject to any duty of confidentiality. It made no difference whether third parties actually had access to its premises.


The public prior use needs to be an enabling disclosure of the features of the claimed subject matter.  Even when the features of the product in question are visible to the naked eye, this is not necessarily enough: in T 1410/14, a vehicle with the claimed features was driven on public roads, but it was not proven the use would have enabled the skilled person to identify all of the features of the invention.  The feature in question was visible only briefly and it was not proven beyond doubt it was clearly and directly apparent to the skilled person.

To whom?

The opponent must show the prior use was made available to the ‘public’.  Was the prior use only made available to those with a bar of confidentiality? If so, this is not a ‘public’ prior use.  For those working in the pharmaceutical field, it is worth noting T 945/09 shows the treatment of a patient is not necessarily carried out with an obligation of confidentiality.
Tip: If defending against a public prior use attack, consider what gaps there may be in the opponent’s attack for each of the above criteria.  A detailed analysis of the alleged prior use may well be missing essential details for the prior use attack to succeed.  If alleging the public prior use, be sure to have all the details clearly laid out for the opposition.  A single missing piece of information may result in the attack failing. 
2.What is the burden of proof for showing a public prior use?

It depends!
If both the patent proprietor and the opponent have equal access to the evidence in question, the applicable standard of proof is the ‘balance of probabilities’ (T 363/96 and T 1776/14).  For example, if the product used as the basis of the public prior use is publicly sold (whether by a third party or the opponent themselves, see T 1748/10), this standard applies.
However, if all of the evidence lies within the power and knowledge of one of the parties, e.g. the opponent (and the patent proprietor has little or no access), the strict standard of ‘up to the hilt’ (T 472/92) must be proven by the opponent, i.e. ‘beyond reasonable doubt’ (T 97/94).
In T 473/13, it was alleged a prior use was made public by the patent proprietor.  In this case, the burden of proof was initially on the patent proprietor to show whether there was a confidentiality agreement, but this shifted to the opponent after the patent proprietor filed a document showing there was at least an implicit duty of confidentiality.
Tip: As the patent proprietor, determine what standard of proof applies as this can have a significant effect on the case. 
3. Are there any different considerations for specific technical fields?
It is worth noting for chemical inventions, the chemical composition of a product forms part of the state of the art when the chemical is available to the public and can be analysed and reproduced by the skilled person, regardless of whether they have reason to do so (e.g., G 1/92). 
If a commercially available product can be analysed using methods known at the priority date and can be reproduced, its chemical composition forms part of the state of the art (e.g., T 301/94).  This is the case even if, before performing that analysis, the skilled person could not have recognised that at least one component was present in the product, or was present in an unusually small amount.
The public prior use needs to be an enabling disclosure to be novelty-destroying.  For example, in T 977/93 the skilled person could not reproduce the polymers without knowing the nature of the catalyst used in the process.
While applicable to all fields, for mechanical inventions in particular, whether the use would have enabled the skilled person to identify all of the features of the invention is imperative to determine. 
Tip: Consider what analytical methods were available to the skilled person at the priority date of the patent and whether the prior use amounts to an enabling disclosure.


There are several hurdles to overcome when making a prior use attack and falling at any one of these will result in the prior use attack failing. Therefore, if you are the one making the attack, it is vital you have all of the information you need. If you are defending, look at poking holes in the opponent’s arguments under each one of these headings.
If you would like further information on any of the above points, or to talk through how they might be relevant to your cases, please do not hesitate to contact Jessica Smart, Kathryn Eldridge or your usual advisor at Kilburn & Strode LLP.

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