Prime Minister David Cameron has declared his "full support" for Culture Secretary Maria Miller after the parliamentary sleaze watchdog opened an inquiry into her expenses.
The Parliamentary Commissioner for Standards' office said John Lyon was looking into a complaint that Mrs Miller claimed more than £90,000 in second home allowances towards the cost of a house where her parents lived.
Mrs Miller has insisted that her expenses were "absolutely as they should be", but the case has ignited hostilities between Downing Street and the press, after Mr Cameron's director of communications Craig Oliver phoned the Daily Telegraph's editor about the story.
Mr Oliver reportedly reminded editor Tony Gallagher during the call that Mrs Miller was in charge of the Government's response to the Leveson report on press regulation.
Number 10 insist he was merely highlighting concerns about the way reporters conducted their investigation into her expenses, rather than attempting to threaten the paper.
Arriving in Brussels for a European Council summit, Mr Cameron said: "Maria Miller does an absolutely excellent job as Culture Secretary and she has my full support. A newspaper has asked her a number of questions. So far as I can see, she has got excellent answers to all those questions. I am sure she will answer them and then get on with her job, which is what she should do."
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.
Labour MP John 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 in 2009 was required to pay back more than £13,000 in expenses claimed on a second home occupied by his parents. In that case, the commissioner said Mr McNulty had effectively "subsidised" his parents from the public purse by allowing them to live rent-free.
But 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.