Oh, I see. In that case, I am not sure why Councillors would need to keep copies of the bank statements out of the office but if they were wanted, redaction would be the way forward on this and using a black marker is very quick and effective!
With regards to the Clerk's reluctance to provide a spreadsheet, I suppose this could be down to a number of issues - perhaps the Clerk is not familiar with excel, or sees this as doubling up of the workload. I don't know if your accounting system allows for the downloading of reports onto a spreadsheet - Sage certainly does and it is fairly painless. However, I don't understand the rationale behind the figures being changed - as you say the accounts package is controlled by the Clerk at all times....
What I would say is that Councillors have a duty of care to the parish to ensure that the accounts and council finances are run appropriately and that the parish council is ultimately responsible for its financial management. Therefore, councillors have a duty to understand the information that is presented to them and if this means that the accounts have to be handwritten on toilet paper, then that is what is required! Therefore to request information on a spreadsheet is perfectly aceptable as long as it doesn't take the Clerk hours and hours of work.