I think this might be current "It is not illegal to buy or sell sex, but sex workers break the law if they loiter and solicit on the streets, keep a brothel (by teaming up at a premises with another woman/women) or advertise their services.
Their clients break the law if they kerb crawl. Legislation passed in 2009 makes it an offence to buy sex from someone "subjected to force, deception or threats". This is designed to clamp down on pimps and traffickers."
Whichever way it falls, the basic fact is that street prostitution is not legal in the UK, and in this case the police are saying, actually we'll turn a blind eye, well more than that we'll give it the thumbs up, as long as you do it over there, out of sight (and out of mind?).