Culture Secretary Jeremy Hunt is under increasing pressure over his relationship with Rupert Murdoch's empire after his special adviser resigned for "overstepping the mark" in contacts with News Corporation's director of public affairs.

Adam Smith stood down after a series of explosive emails released by the Leveson Inquiry into press standards appeared to show Frederic Michel receiving confidential information from Mr Hunt's department.

Mr Smith's resignation merely served to escalate demands for the buck to stop with Mr Hunt himself.

Labour accused the Tories of "sleaze" and called on David Cameron to order an inquiry into whether Mr Hunt had broken the ministerial code.

The party said the rules and regulations ministers are supposed to adhere to clearly stated that they had to take responsibility for the actions of their advisers.

Mr Hunt also faced accusations that he had been too close to Rupert Murdoch and his son James even before he took up his post in 2010.

He met with News Corp executives in New York in 2009 just ahead of them finalising a plan to push ahead with the proposed £8 billion takeover of BSkyB.

Soon after the trip, James Murdoch told David Cameron that his company would back him for Prime Minister.

Mr Smith resigned just hours before Mr Hunt was due to make a statement to MPs.

The Coalition had staunchly insisted that no-one in Mr Hunt's team had behaved improperly as part of the bid proposals, which Mr Hunt was due to decide on a quasi-judicial basis.

Mr Smith resigned, just as Rupert Murdoch was speaking at the inquiry, after admitting that he "went too far".

Mr Hunt told MPs "volume and tone" of the texts and emails between Mr Smith and News Corp lobbyists were clearly not appropriate. But he added that he wanted to set on the record that Mr Smith was a man of "integrity and decency".

Facing down calls for his own resignation, Mr Hunt accused Labour of jumping on a "political bandwagon" over the affair.

Labour leader Ed Miliband had earlier accused the Tory Cabinet minister and his office of "providing a constant stream of information" to the Murdoch empire.

Veteran Labour MP Dennis Skinner also attacked Mr Hunt, one of the Cabinet's billionaires, accusing him of sacrificing his adviser for his own career.

Picking up on Mr Hunt's background and an attack on Mr Cameron earlier in the week, he told the House of Commons: "When posh boys are in trouble, they sack the servants."

Last night Harriet Harman, Labour's deputy leader, wrote to Mr Cameron demanding he urgently refer the allegations to the Independent Adviser on Ministers' Interests, saying there were three apparent breaches of the ministerial code.

It is not the first time that Mr Cameron has faced similar calls about crises to hit his Government. Last year he faced intense criticism over a decision not to refer claims about Adam Werritty, then defence secretary Liam Fox's special adviser.

Both Mr Werritty and Mr Fox later resigned.

Mr Cameron had appeared at Prime Minister's Questions where he initially failed to give Mr Hunt his full backing.

But he later said that he wanted to be "absolutely clear the Culture Secretary had my full support".

Last year News Corp attempted to buy the 61% of BSkyB that it did not already own amid opposition over claims it would reduce media plurality,

Mr Hunt was placed in charge of the decision after Vince Cable was forced to relinquish control after being recorded by undercover journalists saying that he would "wage war" on the Murdoch empire.