Buehler AG v Chronos Richardson Limited

Opposition proceedings before the European Patent Office do not create cause of action estoppel or issue estoppel in later national revocation proceedings. The causes of action are different: opposition concerns maintenance or revocation under the European Patent Convention, whereas national revocation is brought under Patents Act 1977, section 72. More fundamentally, an Opposition Division does not finally and conclusively determine patent validity. The Convention assigns the national courts jurisdiction over infringement and revocation after grant. An unsuccessful opposition therefore does not prevent the same validity allegations being raised in national infringement or revocation proceedings.

Buehler AG appealed against an order of the Patents County Court dismissing its application to strike out Chronos Richardson Ltd’s allegations that the patent was invalid. Chronos had previously opposed the European patent before the European Patent Office, but the Opposition Division rejected that opposition and no appeal was filed.

The appellants argued that the unsuccessful opposition created cause of action estoppel or issue estoppel, because the same invalidity allegations were being repeated as a defence to infringement and in a counterclaim for revocation. The central issue was whether an unsuccessful European Patent Office opposition precluded those allegations in national proceedings.

1. Appeal dismissed. The Patents County Court was right to refuse to strike out the invalidity allegations. The order was upheld, with costs. Leave to appeal to the House of Lords was refused.
2. Cause of action estoppel requires the cause of action in the later proceedings to be identical to that in the earlier proceedings. The infringement defence concerned infringement, while the counterclaim sought revocation of the United Kingdom patent under section 72 of the Patents Act 1977. The Opposition Division had instead determined whether the European patent should be maintained or revoked on the grounds in Articles 100 to 102 of the European Patent Convention. The causes of action were therefore not identical.
3. The distinction was reinforced because section 72 provides grounds of revocation exceeding those available under Article 100. The European Patent Office did not determine infringement, so no estoppel could arise in relation to the infringement defence.
4. More fundamentally, the Opposition Division’s decision was not a final and conclusive judicial determination of patent validity. Opposition is part of the European patent grant process and has an administrative character. The Convention assigns national courts jurisdiction over infringement and revocation after grant. Article 138 preserves revocation under the law of the relevant contracting state.
5. The reasoning in Zahnkranzfraser was applicable: an opposition decision may be important expert evidence, but it has no preclusive legal effect in national revocation proceedings. The domestic authorities were consistent with that structure.
6. Issue estoppel also requires a final judgment. Since the Opposition Division had not finally determined validity, no issue estoppel arose.

• Court of Appeal (Civil Division): The appeal from the Patents County Court was dismissed with costs. Leave to appeal to the House of Lords was refused.
• Patents County Court: His Honour Judge Peter Ford dismissed the application to strike out the invalidity allegations by order dated 13 August 1997.