I cannot see why it is wrong fora man to buy sex, or for a woman to sell it. However, that seems to be the way British puritanism seems to be taking us. (It also seems that it would not be wrong for a woman to buy sex, but that's another debate ... or is it?)
I cannot see how it is fair or just to make sex-hungry males criminally responsible for buying sex from a sex slave when there is no reasonable liklihood that he could discover this other than by making the kind of enquiry the police had thus far failed to make.