Agree with Barmy's ideas.
Book-keeping should be fine, in that it is a transactional task to codify various inputs and outputs into a ledger.
If you are considering doing something more intricate of a financial nature (statutory accounts) as a self-employed individual, it might be best to clarify with the person that you are providing a service to draft the accounts, but that it is their role to check that are satisfied with your draft outputs (in other words, you are providing a service in which they must approve the outputs). If you don't, there could be a danger that you are perceived as providing financial advice. It is the not the FSA that this may concern - merely that if it is used for tax returns, for example, and you happen to make a mistake, there could be a come-back on you. Accountants have professional indemnity to cover situations like this.