David Cameron is under pressure to release private emails exchanged with Rebekah Brooks that he has withheld from the Leveson Inquiry, after extraordinary scenes in the House of Commons in which he refused to answer a question on the issue.
A visibly agitated Mr Cameron was asked during Prime Minister's Questions to tell the Commons why he had not released details of secret messages between him and Ms Brooks, the former News International chief executive, or publicly revealed their existence.
In defiance of parliamentary convention, he flatly refused to tell MPs any more about the messages, which he has not supplied to the Leveson Inquiry into press ethics.
i disclosed this week that Downing Street was sitting on a cache of emails and text messages between the Prime Minister and Ms Brooks, as well as communications with Andy Coulson, the former News of the World editor. Mr Cameron held them back from the judicial inquiry after taking legal advice that they were not relevant to its remit.
In acrimonious Commons clashes, the Prime Minister lost his cool as he was challenged by Chris Bryant, the shadow Home Affairs Minister.
Mr Bryant told Mr Cameron to "stop smiling", adding: "When the truth comes out, the Prime Minister won't be smiling."
Mr Cameron retorted: "Before answering this question, I would like everyone to recall you stood up in this House and read out a whole lot of Leveson information that was under embargo and you were not meant to read out, much of which turned out, about me, to be untrue, and you have never apologised. Until you apologise, I'm not going to answer your questions."
Last night the deputy Labour leader, Harriet Harman, sought to increase the pressure on the Prime Minister by writing a letter to him urging the release of the information.
A senior Conservative Party source added: "Saying 'I'm not going to answer a question' is not acceptable. He does have a duty to answer questions. Otherwise you can only suspect he has something to hide."
Downing Street has stonewalled on the subject of the emails, not denying their existence and repeating that the Prime Minister has co-operated fully with the inquiry.