None of the royals are anywhere near being the richest man in Britain. AFAIK the Queen isn't even the richest woman in Britain.
The murdering, lying, gun-running Nicholas van Hoogstraten was a candidate for the title. Don't know whether he still is, since he got banged up for hiring two guys to assassinate a business rival. But hiring prostitutes would be entirely in his line, since he's a criminal and is so unpleasant he'd be unlikely to get a partner any other way.
And am I the only one who winced at JiK saying
He was upset at having to make a deposit to complete the arrangement