The delays in the European Patent Office in bringing opposition proceedings to an early conclusion can create problems when the patentee wishes to sue for infringement of a patent which is under opposition. Infringement and related proceedings are a matter for national law.

In some countries there is a tendency towards staying infringement proceedings in respect of a patent that is under opposition in the EPO until the opposition has been concluded. This is not the common practice in the United Kingdom. This can lead to complications as shown in the case of Boston Scientific v. Julio C. Palmaz where the plaintiffs sought a declaration of non infringement and revocation of a patent that was contemporaneously the subject of opposition proceedings in the EPO. At the time of the trial, the Appeal Board of the EPO had held that claims that were narrower than those that had originally been granted were patentable over the art cited in the opposition and had remanded the case to the Opposition Division with a direction to allow the case with the amended claims and a description amended to conform with the acceptable claims. However, the final form of the description had not been established and the patent had not yet been reprinted. The judge in the UK case therefore decided that the form of the patent that was before him was that as originally granted and which had been held to be invalid in the EPO.

Consequently, for the patentees to succeed in resisting the revocation action amendment of the British part of the European patent was required. The judge noted that, under UK law, amendment was a matter for the exercise of discretion so that permission to amend could be refused if the patentee had, for example secured a claim he knew to be invalid or where he has delayed unduly in seeking amendment after becoming aware of the need for it. He also noted that the rules in the EPO seemed to make no provision for such factors. Under the circumstances, the judge concluded that, to avoid conflict with the EPO, discretion to allow amendment where there are concurrent proceedings in the EPO should be refused only where the amendment would not result in a valid patent. He then went on to consider whether the amendments accepted by the EPO's Appeal Board would result in a valid patent and concluded that they would not. In the judge's view, the amendments allowed in the EPO added subject matter and this was a ground of invalidity under the European Patent Convention and UK law. In the judge's view the patentees had taken a feature which had been disclosed in the specification only in a particular context and had incorporated it into their claims in a different context. This constituted addition of new matter. Since the amendment was refused and the patent as granted was admittedly invalid, the UK part of the European Patent was revoked.