Prime Minister David Cameron has declared his "full support" for Culture Secretary Maria Miller after the parliamentary sleaze watchdog opened an investigation into her expenses.

The office of John Lyon, the Parliamentary Commissioner for Standards, said he was opening an inquiry following a complaint that Mrs Miller had 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, though Number 10 insisted that 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."