David Cameron has been accused of hiding "incriminating" evidence from the Leveson Inquiry that shows he was "in cahoots" with Rupert Murdoch.
The prime minister has been under pressure to make public a cache of text messages and emails sent between himself and Rebekah Brooks after it was revealed they were not initially handed over to the Leveson inquiry into press ethics.
Speaking during a parliamentary debate on Tuesday morning, Labour MP Chris Bryant said the only reason the Cameron would refuse to publish the material would be if it exposed a past secret deal between News International and the Conservative Party.
Bryant told MPs that the prime minister was "evading" questions put to him in parliament and by the media.
Last month Cameron refused to answer Bryant's question on the issue during prime minister's questions until the Labour MP apologised to him personally for reading out "untrue" allegations about him in parliament.
However Bryant said the prime minister's silence "speaks volumes" and said the public deserved to know whether he had been doing "favours for friends" at News International.
"He is not doing himself any favours," Bryant added. "I can only conclude this material may be incriminating"
Bryant suggested the texts and emails may make "explicit" how Cameron and Brooks were "working together" or that Downing Street was "in cahoots" with News International.
"Or it may be be incriminating if it details the deal that I believe was secured between the Conservative Party and News Corporation before the general election," he said.
Bryant told MPs he thought the Tories had agreed to cut the budget of the BBC in exchange for winning the support of News International newspapers such as the The Sun.
"However long he puts his fingers in his ears and screams 'la la la' and refuses to answers questions, this material will come out."
Bryant added: "It's the cover up that always does for you in the end, this is not going to go away."
Two of the messages have already been disclosed by the Mail on Sunday, Cameron wrote to Brooks: "The horse CB (Charlie Brooks) put me on. Fast, unpredictable and hard to control but fun. DC."
Another message, written by Brooks to Cameron after his speech to his party's 2009 convention, read: "Brilliant speech. I cried twice. Will love `working together'."