Why Is The "illegality" Defence Back In The Spotlight?

It is not uncommon for defendants to professional negligence claims to argue that the claimant should be barred from recovering damages because his or her cause of action is tarred by illegality. However, over recent years, the law has taken a variety of approaches to when illegality will provide a defence. With the issue about to come before the Supreme Court again, Helen Evans and Ian McDonald of 4 New Square explain.

What is the relevant test for illegality and where does it come from?

Until 2016, the defence only worked if the defendant could show that the claimant had to rely on the illegality in order to bring the claim: Tinsley v Milligan [1994] 1 AC 340. In Patel v Mirza [2016] UKSC 42, the Supreme Court decided that this approach was too formulaic.