It emerged yesterday that Mary Anne Thompson's resignation on Monday followed the State Services Commission decision to refer to the police what it said were "serious questions" about qualifications Ms Thompson claimed to have when applying for senior roles in the public service.
The allegations are believed to concern a PhD from the London School of Economics which Ms Thompson has previously listed among her qualifications but of which the Department of Labour has no record.
Last night, the London School of Economics said it had no record of a Mary Anne Thompson having gained a PhD.
Ms Thompson's tenure as immigration boss was already under a cloud because of help she gave to relatives to get residency in New Zealand in 2005.
That is now also part of a separate investigation by the SSC, after the details were made public.
In Parliament yesterday, Deputy Prime Minister Dr Michael Cullen said the credentials under question were from 1990 and again in 1998, when Ms Thompson was appointed to the Department of Prime Minister and Cabinet (DPMC).
In 1990, Ms Thompson was appointed as chief economic adviser with the Department of Maori Affairs.
The Department of Labour has no CV on file for Ms Thompson and a spokesman said there was no record of her claiming to have a PhD.
Treasury - where Ms Thompson worked from 1992 - said it destroyed employment files after 10 years and also no longer had Ms Thompson's records.
However, Ms Thompson had included the PhD in information she gave media after she was appointed as Treasury's adviser to Winston Peters in 1996.
The investigation could see some high-profile public servants questioned about Ms Thompson's job interviews.
Current State Services Commissioner Mark Prebble was Ms Thompson's boss for most of her time in the DPMC and has delegated the SSC investigation because of their previous working relationship.
Depending on the scale of any breach, the consequences for Ms Thompson could be serious.
In 2002, John Davy was jailed for fraud after he admitted there were several fabrications in his CV for the job as head of the Maori Television Service.
