Appointment of the Comptroller and Auditor General

There is widespread agreement that there should be a time limit, and Sir John Bourn himself thinks so, but does the right hon. Gentleman accept that it should be longer rather than shorter? In the US, the Budget and Accounting Act 1921 sets a term limit of 15 years for the equivalent post there. That may be a little long, but might not a limit of only five or six years be too short?