Hi and welcome
I'm an indi and do my own tax returns. I state my profession as "escort" and have done for the last few years and had no problems with the IR (fingers crossed).
The on-line forms are pretty straightforward in my opinion and if you do get stuck the Inland Revenue helpline tend to be very helpful so that's why I do mine myself.
Each tax year I buy a 12 section folder (from smiths, tescos etc) and I've labelled it up for each month in the tax year from april to march and I just put my receipts in each bit. I keep receipts from hotel visits, condom shopping, taxis, phone bills etc. If I pay for anything on credit card I keep a copy the statement for that month in the folder too.
I bank all my cash in my personal account and keep a spreadsheet of what I have earnt each month and so refer to those two things at the end of the year as regards income.
As regards expenses, I just again use a spreadsheet using everything in my receipts file and adding it under the relevent section on the tax form - admin costs, travel etc.
The on-line tax form works out everything for you once you have input your ins and outs so if you keep a record of money earnt and keep all your receipts in one place then it is pretty straightforward to do yourself but an accountant may know of more loopholes and tax saving methods so it my be worth using one just for that reason - their costs are tax deductable I believe.
The www.hmrc.gov.uk site is very useful and they will send you out a folder full of info for newly self employed peeps if you ask. They run seminars as well to help people and you may also be able to get free advice from local business/enterprise groups - look in yellow pages for one near you.
I think it is still the case that you have to register with the IR within 3 months of starting out and you will need to pay class 2 National Insurance contributions every week (I do a monthly direct debit from my bank account). At the end of the tax year you have to, in addition to your class 2s and your tax bill, pay Class 4 National Insurance contributions - the amount of which is based on your earnings and can be quite high.
So its get registered, start paying class 2 NI conts, then keep records of ins and outs and then fill in your return by the end of Jan each year - oh and then pay the damm bill!
Hope that helps and welcome to SAAFE.