Hi Roxy, firstly all you need do is go on the HMRC and register as self-employed, if you are concerned about declaring yourself as an escort/webcammer you dont have to, lots of escorts use their "normal" business, or you can be a counsellor, therapist or entertainer. Escorting by yourself is not a crime and perfectly lawful and the revenue,HMRC are more interested in catching those who arent registered, then they use a draconian method of calculating your back-tax, ie hourly rate ?120X 40 hours, which, ofcourse we know is unrealistic.
After that, usual self-employed rules apply if you under-estimate your earnings and they can prove otherwise with your assets, (and a tax inspector once told me the biggest sourse of investigations is people "dobbing" others in!
No, you dont need to keep address, clients numbers or anything else, just like any "cash" business, if you go to the hairdressers they arent going to ask your details!
A simple notebook to keep the most basic of records (a page a day diary is ok for simple work) each day record your "sales" in one column, then any "expenses"=final profit/loss for each week, then do the same till end of tax year, then you you will get a simplified self-assessment form to return with totals, and they work out your tax n.i. , you pay class 2 N.I, then class 4 after ?16.000-(thats what the Govt has just put up)-but its in your own interest, as if you are going to do this for a long time, it credits you towards benefits/state pension in the future.
Two big advantages of doing this is 1. you cant be blackmailed by clients etc,and 2. you have to keep your books for six years, its very handy to refer to each week to see what it was like last year, so can plan your holidays during quiet times.