Nick,
Joxster has it about right. Having been a contract for near on 10 years now it’s very simple.
You’ll require a LTD company and the only decision after that is whether you’re going to attempt to dodge ‘IR35’ – the legislation used to max high earning self employed contractors pay more tax.
The answer to whether to dodge IR35 is purely up to you but what I can say if you get a good accountant not a shrinked-wrapped package from some faceless accountancy firm they will probably be able to advise you better than anyone else, my accountant offers both services – one to dodge IR35 and one to not, obviously the one attempting to dodge costs a lot more.
As for umbrella companies forget it a compelte waste of time and money, you might think your saving money but they are useless when you step outside of their comfort zone…
Also insurance against IR35 IMO is waste of money as well – i can’t be bothered getting my contract checked everyone month, 3 months etc. If the government wants to get you for missing tax they will.
Ollie