PSAA is not a prescribed person under the Public Interest Disclosure Act.
PSAA is however referred to in the following paragraph from Blowing the whistle to a prescribed person: List of prescribed persons and bodies published by the Department for Business Innovation and Skills:
Local authorities (England)
Following the Audit Commission’s closure on 31 March 2015, disclosures relating to local authorities can be made to the external auditor of the relevant authority or the Comptroller and Auditor General. To make a disclosure to the authority’s external auditor, please contact the local authority, who will have a record of who to contact. You can also ask Public Sector Audit Appointments Limited (PSAA), the company now responsible for appointing auditors to local government and police bodies (https://www.psaa.co.uk ) for the name of the auditor of the relevant local authority. It should be noted that PSAA is not a prescribed person under the Public Interest Disclosure Act and their role in this is only to signpost individuals to the external auditor appointed to the local authority in question. To make a disclosure to the Comptroller and Auditor General, please contact the National Audit Office.