Australian Information Commissioner John McMillan has been appointed by the state government to complete NSW Ombudsman Bruce Barbour's investigation into a long-running police bugging scandal.

But the announcement that Professor McMillan – a former Commonwealth ombudsman – will be "acting" NSW ombudsman for two years after Mr Barbour leaves on June 30 has drawn criticism.

Premier Mike Baird said the "acting" appointment was at Professor McMillan's request, and because he is aged 65.

A spokesman explained legislation prevented the appointment of an ombudsman aged 65 or over so the "acting" appointment secured Professor McMillan's services.

However, Labor's Adam Searle said while Professor McMillan was undoubtedly qualified, the office "