But the guy never even checked my receipts or statements.
I used to work for a firm of accountants, and the only time your receipts would be checked is if an audit was being performed, and even then, only a sample would be.
You are paying them to prepare statements from YOUR records, not to check that you've recorded everthing correctly. After all, why should they do that? That would take ages (and therefore cost you a fortune) £700 sounds pretty reasonable for a chartered accountant, and window cleaners are small fry to them.
-Philip