Bonkors,
This post will soon fill up with members saying, 'Don't be stooopid, get an accountant', or 'an accountant will save you more money than you spend on them', or 'Focus on your business and let an accountant do the boring stuff'.
But if you're a sole trader, doing your own books is easy; an accountant won't save you anything; though they'll make out they do.
A good book which is available in the library is called 'Self Assessment for the Self Employed', it's up-dated each year. Self assessment is easy to understand; I think some window cleaners think it's rocket science when it's not.
And remember, it's called 'Self Assessment', not 'Accountancy Assessment'.