This chapter shows that decision of the UK Supreme Court in Patel v Mirza, undoubtedly the most important case on illegality in contract for many years. In Patel v Mirza, Lord Toulson, delivering the judgement of the majority, gave a very full account of Lord Wilson's judgment without any hint of criticism. Perhaps the first thing to say about Patel v Mirza is that it was decided by Supreme Court of nine judges. In England lower courts will surely seek to follow Lord Toulson; the possibility of a rerun in the Supreme Court cannot be excluded. Courts would be required to make a value judgement, by reference to a widely spread melange of ingredients, about the overall "merits" or strengths, in a highly unspecific non-legal sense, of the respective claims of the public interest and of each of the parties.