There is some kind of non-official red corner close to Paddington station in London, people get arrested all the times there for talking to undercover prostitutes who are actually police officers.
Why would they get arrested when prostitution is legal in The UK?
Prostitution is legal in the UK, but soliciting prostitution in a public place is still illegal, as are a host of other related crimes.
Source: https://en.wikipedia.org/wiki/Prostitution_in_the_United_Kingdom
Frequently in any business, you need to follow specific laws designed to prevent some of the issues around that business that are undesirable in some way. For example, banks have anti-money-laundering laws even though banking is legal.
In Great Britain (England, Wales and Scotland), prostitution itself (the exchange of sexual services for money) is legal,[2] but a number of related activities, including soliciting in a public place, kerb crawling, owning or managing a brothel, pimping and pandering, are crimes.
https://en.m.wikipedia.org/wiki/Prostitution_in_the_United_Kingdom
