I just read a where Bernadette, the Dominatrix/BDSM teacher explains how the law works when it comes to spanking in the UK. An no person, an adult included, can consent to being spanked. People have gone go jail for the crime I the past. But, there was a case where an adult got away with encouraging two minors into whipping themselves on the back with a zanjeer (a whip with a number of tails with bladed fixed to the ends). They got away with it because the underage boys did the harm to themselves.