Mr Whittingdale said he had been unaware of the woman’s occupation and had broken off the relationship after six months in 2014 when he discovered someone was trying to sell the story to the press.
Labour’s shadow culture secretary Maria Eagle said it was now essential for Mr Whittingdale to give up his responsibilities for press regulation to ensure there was no perception of “undue influence” in his dealings with newspapers.
But a Downing Street spokesman said: “The Prime Minister has got full confidence in John Whittingdale to carry out all of his duties.” The Number 10 spokesman confirmed that Mr Whittingdale did not inform Mr Cameron about press interest in his relationship at the time he was appointed to the Cabinet after the 2015 general election.
The Prime Minister learned about the affair only around ten days ago, when the story emerged on the internet, said the spokesman. He said it was a decision for Mr Whittingdale whether he felt it necessary to inform the PM about the issue.
In a statement last night, Mr Whittingdale insisted that events had no bearing on any decisions he took in office.
“This is an old story which was a bit embarrassing at the time. The events occurred long before I took up my present position and it has never had any influence on the decisions I have made as Culture Secretary,” he said.
BBC2’s Newsnight reported that four newspapers – The People, The Mail on Sunday, The Sun and The Independent – had investigated the claims at the time but concluded it was not a public interest story.
Although the relationship occurred before he was made a minister, it occurred at a time when he was chairman of the Commons culture, media and sport committee, which held a series of hearings on the phone-hacking scandal.
Ms Eagle said: “Everyone is entitled to a private life. However, these revelations raise serious questions about why the Secretary of State has reneged on the government’s promise to deliver the cross-party agreement on Leveson when this is something he was previously committed to as chair of the culture, media and sport Select Committee.”
Brian Cathcart, from the Hacked Off campaign group, said since becoming Culture Secretary, Mr Whittingdale had taken a number of decisions which had been welcomed by the press.