I understand why some people think it's a bad idea to have first-time sex with a prostitute, rather than with someone you manage to pull at a pub or club. But I wish my first experience had been with a really good professional. As a virgin, you're going to be nervous as hell, regardless of whether you're with an amateur or a professional. But if you choose the right professional, she will help you handle your nerves (rather than, possibly, add to them), and she will do everything possible to ensure that you enjoy your first experience and that you look back on it as a success and not a humiliating failure. This will help you develop confidence and with luck, start you off on a long and happy sexual career!
The key to it is choosing the right professional and I can't help on this. I punt in the south west and have no knowledge of the London scene. But if you study AW carefully, you ought to be able to identify someone who will give you a great time. General suggestions; choose someone older than you, perhaps mid to late 30s. Choose someone who has been offering sexual services for at least three or four years. Choose someone with plenty of good feedback/FRs from punters who themselves have plenty of favourable feedback. Finally, choose someone you really find attractive.
Good luck, and enjoy!