I'm an accountant. In Scotland though so not miuch good to you. Here's some free info though:
If you're self-employed on a sole trader basis (which is how it sounds), you need to notify the tax office straight away as you've probably already passed the deadline date. You'll get a £50 fine which they MAY enforce. IME they seldom do.
You're probably not going to have any tax to pay until January 2011 but you should be making provision already. As said above, premium bonds is a good idea but so is a separaste bank account.
If you don't fancy using accounting software get a spreadsheet template which records your income and outgoings.
Keep a separate bank account for all business transactions. Doesn't strictly need to be a business account as long as it is kept separate.
Yes, you should get an accountant and I'd do it now. Make sure you pick one who (a) comes recommended, and (b) works on a fixed price basis. You should expect to pay anywhere between £400 and £1,000 p.a. depending on what you need. Remember an accountant is an expert so use them as such. The money you spend on them should be for business advice and tax planning etc not sorting thru bags of petrol receipts.
Disclaimer: I only deal with ltd co contractors now so some of the above might be outdated.