In the version of the same document for 2023 I also found this:
There are various ways for an authority to source an internal audit service, for example:
● Purchasing an internal audit service from a local firm or specialist internal audit practice with an understanding of the local government legal framework
● Purchasing an internal audit service from a principal local authority
● Engaging a competent internal auditor with sufficient organisational independence to undertake the role
● Appointing a local individual or a member of a panel of individuals administered by a local association affiliated to NALC, SLCC or ADA
So, this says it's fine. But it seems contradictory to the other statement above which is still in the 2023 edition. The assumption seems to be that the ALC must be sufficiently independent, despite it also probably providing other services to a council.
ALC's also have the stated aim of "protecting and promote the interests, rights, functions and privileges of members [ie. councils]". Also, supporting the "corporate interests" of councils. One could could argue that a proper and complete audit is in the interests of a council. On the other hand, an org involved in providing advice to a council on matters covered by the audit might take the view that it is not in the interests of the council and/or the ALC to highlight all the areas for improvement. It might be in the public interest, but not in the council's interest or the ALC's. Am I wrong?