Safestand Limited v Weston Homes PLC & Ors

A party is not bound by every formulation advanced at an earlier patent trial. The doctrine of approbate and reprobate requires a clear and unequivocal election between inconsistent positions, followed by conduct inconsistent with that election. A formulation advanced in the earlier proceedings is not necessarily an election where the party must now plead infringement consistently with the court’s findings, subject to appeal.

A Formstein defence cannot be used to reopen an issue necessarily decided in earlier proceedings between the same parties. Nor may a party revive a prior-use allegation which could and should have been pleaded for the original trial where doing so would create a further, substantial trial. That conduct remains an abuse of process under the rule in Henderson v Henderson.

The claimant had previously obtained judgment that three patents were valid and infringed by the defendants’ builders’ trestles. The defendants later modified the trestles and kickboard brackets and sought declarations of non-infringement in relation to two surviving patents.

The claimant alleged infringement by equivalents. The defendants advanced Formstein defences based on Kelk and an alleged prior disclosure by the claimant. Each side applied to strike out the other’s case. The issues were whether the claimant was precluded from reformulating the inventive concepts relied on for equivalence, and whether the defendants could reopen issues concerning prior art and prior use.

1. Weston’s application. The defendants’ application to strike out the claimant’s equivalence case was dismissed. The claimant had modified its formulations of the inventive concepts, but its earlier formulations did not amount to a binding election between inconsistent options. The relevant doctrine requires a clear and unequivocal election, usually involving a benefit, and subsequent conduct inconsistent with that election. The claimant’s case now had to be advanced consistently with the court’s earlier findings, subject to any appeal. Its new formulations were arguable and had to proceed to trial.
2. Kelk. The claimant’s application to strike out the Formstein defence based on Kelk succeeded. The earlier judgment had necessarily decided that a skilled person reading Kelk would not have contemplated a trestle with a selectively removable safety barrier on the working side. That issue was a necessary ingredient in the conclusion that EP 738 was not obvious over Kelk. A Formstein defence relying on the same issue would require it to be reopened. The developing nature of Formstein in the jurisdiction did not override the established law of issue estoppel, and no special circumstances causing injustice were shown.
3. Safestand Prior Disclosure. The claimant’s application also succeeded on this limb. The defendants could not relitigate an allegation of prior use which the court had already found could and should have been pleaded in time for the substantive trial. Although a second trial on the declarations of non-infringement would occur in any event, adding the prior-use issue would create a substantial trial involving significant evidence, argument and court time. The vice addressed by the rule in Henderson v Henderson therefore remained, and permitting the defence would be an abuse of process.
4. The defendants’ Formstein defences were struck out. The claimant’s equivalence case was not struck out.