Make a request under the Data Protection Act (199

informing them that they have 40 days to comply or you will inform the information commissioner of their failure to comply with the law. If they are of any doubt that the information is covered by the act, point them at the Durant vs. FSA case, where the judge ruled that bank statement information is indeed personal information and thus covered by the Data Protection Act.
The maximum they can charge you is £10 - I had no trouble getting this information from Barclays - they just sent it straight away and they didn't ask for any payment.
They tried to catch me out by sending my 10 years instead of the requested 6 - probably in hope that I would start a claim for the full 10 years, which they would probably have had no trouble striking out.