Have you read through the Hmrc website? Thats probable the best place to find this information.
If I remember correctly its just a couple of basic questions (when I did mine I left the company name part blank, and was registered no problem) not like a 10 page survey and you can put whatever you want ie escort, stripper, therapist, model, coach of some sort etc, just make sure whatever you pick is the same as what you tell your bank or accountant.