I am paying about £200.
I keep my own records and just give the accountant the figures once a year.
The accountant fills in the self-assessment for me and submits it to the Inland Revenue - yes, I could do that myself, but by doing it this way, they are available for any questions and available to give me a reference (which you might need if you get a mortgage).
You don't need to say you do a sexual service. Say you are a therapist, a counsellor, an artist, a spiritualist! Anything that works for you.
I am a qualified therapist so that works for me.