I think as far as official stuff goes, you just need to be declaring your income to HMRC. The simplest way to do it is to register as self-employed, although you might decide you want set up as limited company. You can get advice from HMRC and/or an accountant. Your escorts won't be employees, which makes things simpler, but someone who answers the phone may be an employee and in that case you'll need to set up NI contributions and things.

Remember that running an escort agency is illegal, and not discussing sex might not get you off the hook. As long as you pay your taxes and don't work with escorts who are underage or illegal, you'll probably be left alone, but do your research so you can stay out of trouble.