Im considering doing it myself ... is it that hard?
Matt 
Matt,
It's very simple to do if you're a sole trader earning under the VAT threshold. I'd suggest you visit your local library and get the book, 'Self Assessment for the Self Employed'; it's updated every year, but last years will be pretty much the same as this years.
It may sound daunting, but it's not. I reckon if you donated just one-day of your life to finding out how it all works, you'll save yourself a small fortune.
And for those of you who reckon that because, for example, an accountant charges you £200; you'll pay £200 less tax; well that's perfectly correct.
But you've still paid out £200! But if that £200 was counted as profit, you'd have only paid out the tax owed on £200; about £50 at the most (as long as you're not on the 40% tax threshold, which only a minority of window cleaners will be on).
So you're still £150 out-of-pocket, for something that's really very simple to do.