A simple outline of the rules is at gov.uk/expenses-if-youre-self-employed/overview
Interesting phrases include 'Allowable expenses don?t include money taken from your business to pay for private purchase' - good luck trying to argue that this wasn't a private purchase: regardless of your work, you needed to do something and the choice was the same. Escorting may have given you the money to pay for the implants, but it's clearly not a business purchase.
(Even though it's not, imagine it was. Then you see 'If you use something for both business and personal reasons, you can only claim allowable expenses for the business costs'. So you spend, oh, an hour a day kissing / sucking clients - you would only be able to claim 1/24th of the cost.)
Similarly, you can't claim for gym fees or everyday clothing even if you do use the benefits of both at work.