Your tax return is basicaly a profit and loss account. This shows how much you made in the year.
A weekly cash flow has nothing to do with this, but it can show how you were able to pay money in the bank, go on holiday etc. For instance, say one week you paid £1,500 cash in the bank, where did it come from?
Your end of year returns are probably fine. The question you need to ask your accountant is what kind of records do you need to keep and in what detail.