Labour has stepped up demands for Jeremy Hunt to be sacked, amid fresh claims he colluded with Rupert Murdoch's empire in a bid to prevent a public inquiry into phone hacking.
A newly-disclosed email from News Corporation public affairs executive Fred Michel said the embattled Culture Secretary wanted the firm to "guide his and Number 10's positioning" on the scandal.
It also boasted of a tip-off about an "extremely helpful" statement Mr Hunt was due to make to MPs on the BSkyB bid.
Following the disclosure, in material released to the Leveson Inquiry by former News International boss Rebekah Brooks, Labour said David Cameron must act to get rid of Mr Hunt.
"This is absolutely not acceptable," said Labour deputy leader Harriet Harman. "How much more evidence does David Cameron need that this man is not fit to hold this high office?"
But a spokeswoman for Mr Hunt insisted that Mr Michel's only contacts were with his special adviser, Adam Smith, who has already resigned after admitting his relations with News Corporation were too close.
The Culture Secretary acted with integrity throughout and will "vindicate" his position when he gives his evidence to the inquiry, according to the spokeswoman.
Ms Harman said: "Clearly there was complete collusion between the Secretary of State and his office and News Corp on a bid where he was supposed to be impartial, which is why he should not be in his job. Either he didn't know what was going on on an £8 billion bid, in which case he shouldn't be in his job and he should be sacked, or he did know and he is covering up and blaming everybody else, in which case he should be sacked."
But a spokeswoman for Mr Hunt insisted: "Jeremy Hunt will respond to this when he gives evidence to the Leveson Inquiry in due course. He is confident his evidence will vindicate the position that he has behaved with integrity on every issue. It has already been made clear that when Fred Michel has claimed in emails to be speaking to Jeremy Hunt that was not the case.
"On July 11 2011 Jeremy Hunt wrote to Ofcom for further advice about the impact of phone hacking on the BSkyB bid."