In reply to Tall Clare:
I'm a director and employed by my own company (limited), but I'm not classed as self employed.
being limited has the advantage of separating the company money from your own assets (which is very hard to get you head around at first - if you make a good profit. The money isn't yours!!)
Being limited means you have to file accounts, which usually means an accountant which costs money, but depending on what you are intending doing and how much you are prepared to do yourself (accounts wise) can be relatively cheap.
Other than that £14 a year to companies house and of course corporation tax on your profits and possibly VAT
"Working for yourself gives you the freedom to work all the time!!" If you work out your hourly rate you'd be better off with a paper-round.
PM me if I can help more.
Tax Assist are prety good with advice and are middle priced accountants.