The expenses investigation facing Maria Miller follows a complaint that she claimed more than £90,000 in second home allowances towards the cost of a house where her parents lived.
The complaint was lodged earlier this week by Labour MP John Mann, who claimed the arrangement was "identical" to that of former Labour minister Tony McNulty.
Mr McNulty was required to pay back more than £13,000 in expenses two years ago, after being found to have effectively "subsidised" his parents from the public purse by allowing them to live rent free in a second home.
Earlier this week Mrs Miller insisted that all of her expenses were "absolutely as they should be" in response to an article in The Daily Telegraph that reported the claims.
David Cameron gives his backing to Culture Secretary Maria Miller after a Parliamentary watchdog launches an investigation of her expenses.
The Prime Minister's spokesman insisted he has confidence in his Culture Secretary Maria Miller amid a spat with the Daily Telegraph.