Information Powers: TMA70/S19A, TMA70/SCH1A/PARA 6 and FA98/SCH18/PARA 27: Private Accounts - Timing of Notice
Since there is no hard and fast rule about whether you can obtain access to private bank account documents, there can equally be no hard and fast rule about the stage of the enquiry at which any notice requiring them should be issued. The case for examining such documents may change as the enquiry progresses.
In some cases you may feel confident that you can reasonably require private bank account documents at the opening of the enquiry.
In other cases you may need further information about the accounts before you can decide, or it may depend on what you find in the course of your examination of other records.