This is a dangerous thread to reply to! 😯 But here goes…
Prostitution is not, in or of itself, illegal (neither is escorting, irrespective of whether that includes prostitution). Pretty much everything else around it is though (pimping / living off immoral earnings / running a brothel / soliciting etc).
As for the alleged income, any specific google search (.co.uk) for such activity will quickly show that the rates are not consistent with what you are being told (a qualified masseuse, only offering genuine relaxing massage / aromatherapy etc, can easily obtain more than £20 per half hour). Income from such activity is fully taxable. And the, er, expenses are deductable as usual….
Regards