In Patel v Mirza [2016] UKSC 42 a panel of nine judges were asked when illegality should bar a claim.

The question goes back almost 250 years to the case of Holman v Johnson (1775) where Lord Mansfield said "no court will lend its aid to a man who founds his cause of action upon an immoral or an illegal act". This strict principle has however been loosened over the years and now the Supreme Court must define clear rules.