The cabinet minister at the centre of claims that aides threatened a newspaper with the Leveson press reforms as it prepared to publish a story about her expenses is to face an investigation.

John Lyon, Parliamentary Commissioner for Standards, is looking into a complaint that Culture Secretary Maria Miller claimed more than £90,000 in second home allowances towards the cost of a house where her parents lived.

Last night, Prime Minister David Cameron declared the minister had his full support.

Mrs Miller has also insisted her expenses were "absolutely as they should be".

However, Labour increased its pressure on her by claiming the Government wanted to threaten the press in order to control the news agenda.

Earlier this week, it was reported Mr Cameron's director of communications had phoned the editor of the Daily Telegraph about the story and reminded him Mrs Miller was in charge of the Government's response to Leveson's calls for press regulation.

Number 10 insisted they were merely highlighting concerns about the way reporters had conducted their investigation into the minister's expenses.