What standards in respect of document creation and retention it requires of external bodies undertaking audit work in the public sector.

This is a matter for Audit Scotland. Audit Scotland was established under the Public Finance and Accountability (Scotland) Act 2000 to provide audit services on behalf of the Auditor General for Scotland and the Accounts Commission. Audit Scotland is therefore responsible to them for the performance of these duties.
Section 69 of the Scotland Act 1998 provides for the appointment of an Auditor General for Scotland. Section 69 (4) provides that the Auditor General for Scotland shall not, in the exercise of any of his functions, be subject to the direction or control of any member of the Scottish Executive or of the Parliament.