Ex turpi causa

It was an established principle that the court would not award compensation under a cross-undertaking for the loss sustained by an unlawful business or where the beneficiary of the cross-undertaking had to rely to a substantial extent upon his own illegality in order to establish the loss.

As a matter of international comity, it did not matter for that purpose whether the acts in question were unlawful under English law or under foreign law. That principle was subject to the qualification that the unlawfulness had to be sufficiently serious to engage the ex turpi causa rule.

What was sufficiently serious depended on the circumstances of the case, and in particular the state of knowledge of the claimant under the cross-undertaking at the relevant time; but the claimant’s conduct had to be assessed having regard to the fact that the claim was for compensation under a cross-undertaking.