Labour MPs quiz Defence Secretary Liam Fox about his friendship with a man who allegedly claims to be one of his advisers and has visited him at the Ministry of Defence on many occasions.

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Former armed forces minister Kevan Jones told the Guardian that Dr Fox's unrecorded meetings with Adam Werritty could pose "a threat to national security" if they discussed classified material.

Dr Fox and Mr Werritty are pictured together here during a visit to Sri Lanka in 2009 on the Sunday Leader website.

Mr Jones said he was also concerned that Mr Werritty, who used to share a flat with Dr Fox and was best man at his wedding in 2005, may have been seeking to benefit financially from the friendship.

At the Conservative conference in Manchester today, Dr Fox refused to discuss the issue with Channel 4 News Political Correspondent Michael Crick.

Meetings at MoD

Dr Fox said in a written parliamentary answer to Labour MP John Mann that he had met Mr Werritty 14 times at the MoD in the last 16 months, "but not in an official capacity".

Mr Werritty is not an official special adviser to Dr Fox, but according to the Guardian, he says he is an "adviser to Rt Hon Dr Liam Fox MP" on his business cards.

Mr Mann also asked Dr Fox how many times Mr Werritty had travelled with him on overseas visits since May 2010. Dr Fox answered: "Mr Werritty is not an employee of the Ministry of Defence and has, therefore, not travelled with me on any official overseas visits."

An MOD spokesman said: "Adam Werritty is not an MoD employee. He is a friend of the secretary of state. Mr. Werritty is not and has never has been part of Dr Fox's official travelling party when the secretary of state is abroad on official business. In line with MoD guidelines the department only covers the costs of its employees."

This is becoming a very murky business indeed. Shadow Defence Secretary Jim Murphy

Shadow Defence Secretary Jim Murphy told the Guardian "This is becoming a very murky business indeed. People will be surprised by these new revelations. Liam Fox has questions to answer. He and Mr Werritty should publish all emails between themselves relating to MoD business."

The Guardian said that when Dr Fox was shadow defence secretary, Mr Werritty was a director of a company called Security Futures and accompanied him to meetings in the US, Middle East and Sri Lanka. It also alleged that when Dr Fox was shadow health secretary, Mr Werritty ran a health consultancy firm.

The newspaper said a meeting Mr Werritty brokered in the Middle East had led to the defence secretary being dragged into a blackmail lawsuit that could lead to Dr Fox having to give evidence in an American court.

Sri Lanka

In December 2010, Channel 4 News online reported on Dr Fox's postponement of a private trip he had planned to Sri Lanka, which was facing war crimes allegations.

Foreign Affairs Correspondent Jonathan Miller wrote: "Dr Fox, who has had close relations with successive Sri Lankan governments for more than a decade, had been due to deliver a memorial lecture at the invitation of the widow of a former foreign minister, killed by the Liberation Tigers of Tamil Eelam five years ago.

"The defence secretary made five trips to Sri Lanka in the past three years, all while in opposition. Each trip was paid for by the Sri Lankan government. On 2 December, the defence secretary held a private meeting with Sri Lankan President Mahinda Rajapaksa in London's Dorchester Hotel, while he was on a private visit to Britain.

"The visit was aborted when a Tamil pressure group sought the arrest of one his entourage on war crimes charges. The meeting was portrayed by the Sri Lankan government as a diplomatic coup on its official websites, which displayed prominent pictures of the President and Dr Fox warmly shaking hands.

"Among matters reportedly discussed between the two were investment opportunities in the north of the island, where many of the alleged atrocities took place."