Parliament's sleaze watchdog is beginning an investigation into claims that Culture Secretary Maria Miller wrongly used her MP's second home allowance to pay for a house where her parents lived.
Prime Minister David Cameron on Thursday declared his "full support" for Mrs Miller after Parliamentary Standards Commissioner John Lyon announced he was launching a probe following a complaint from Labour MP John Mann.
The affair has prompted a war of words between Number 10 and Fleet Street after two Government aides who contacted the Daily Telegraph to discuss a story it was planning to run on Mrs Miller's expenses claims both mentioned her role in the official response to the Leveson Report on press regulation.
The Telegraph on Friday published a blow-by-blow account of its investigation and the Government's response, detailing calls made to the paper by Mrs Miller's special adviser Joanna Hindley and Mr Cameron's director of communications Craig Oliver.
Number 10 has insisted that their references to Leveson when discussing the case were intended to reflect how busy Mrs Miller had been and the concerns she had about her elderly father being "doorstepped" by a reporter, and did not amount to an attempt to threaten the paper.
Mrs Miller claimed second home allowances of £90,718 - almost the maximum permitted - between 2005 and 2009 towards mortgage payments, bills and other costs relating to a house where her parents had apparently been living since 1996.
Mr Mann complained to Mr Lyon earlier this week about the arrangements, which he said were "identical" to those of former Labour minister Tony McNulty, who was required to pay back more than £13,000 after the commissioner ruled he had "subsidised" his parents from the public purse by allowing them to live rent-free.
A spokesman for the Culture Secretary said: "Mrs Miller's expenses have been audited twice and found to be wholly proper and above board. Any suggestion to the contrary is simply untrue."
The Basingstoke MP was ready to "fully co-operate" with any inquiry, said the spokesman. In an interview with the Evening Standard, Mrs Miller said one of the two audits was carried out by former civil servant Sir Thomas Legg - who was called in to review all MPs' claims at the height of the expenses scandal - and the other by the Conservative Party.
Asked whether Sir Thomas was aware that her parents were living at her designated second home, Mrs Miller said: "I obviously spoke to the fees office about my claims and they were happy that everything was in order."