Accusations about national security threat put to minister over Adam Werritty, who presents himself as an official adviser

Liam Fox, the defence secretary, has been accused of putting national security at risk by allowing a close personal friend, who presents himself as an official adviser, access to the Ministry of Defence.

MPs have raised concerns that Adam Werritty has introduced himself as the defence secretary's adviser in order to gain information for financial gain. Werritty, who is not a government employee, hands out business cards with the portcullis logo that describe him as an "adviser to Rt Hon Dr Liam Fox MP".

One meeting that Werritty brokered in the Middle East has led to the defence secretary being dragged into a US blackmail lawsuit that is likely to lead to Fox being called to give evidence in a US court.

Werritty, a former flatmate of Fox, was best man at the minister's wedding in 2005. He has visited Fox at the MoD's building in Whitehall 14 times in the past 16 months, a Freedom of Information request shows. Werritty is planning to be in the auditorium when the defence secretary speaks at the Conservative party conference in Manchester on Wednesday.

Werritty has not been given security clearance and the MoD confirmed he was not an official adviser to Fox or a government employee in any capacity.

Kevan Jones, a former armed services minister, told the Guardian that Fox's unrecorded meetings with Werritty could pose "a threat to national security" if the pair discussed classified material.

Jim Murphy, the shadow defence secretary, said: "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."

Murphy has asked Fox if Werritty is employed in any capacity or in receipt of any funds. Fox has not replied to Murphy's written questions sent a month ago.

Michael Dugher, parliamentary private secretary to Ed Miliband and a shadow defence minister, said the links between Fox and Werritty were "alarming" and "worrying".

Questions have been raised about whether Werritty is seeking to profit financially from his links to Fox.

While Fox was shadow defence secretary from 2005 onwards, Werritty was a director of a company called Security Futures. Werritty accompanied him to several high-profile meetings, including dealings with politicians in the US, the Middle East and Sri Lanka.

And, while Fox was shadow health secretary from 1999 and 2003, Werritty ran a health consultancy company.

Jones said: "It raises question about whether Werritty was looking to financially gain from their relationship."

The MoD refused to explain why Fox appeared to rely on the advice of a close friend rather than his team of highly-trained officials.

In a written parliamentary answer, Fox said: "I have met Mr Werritty 14 times at the Ministry of Defence main building over the past 16 months but not in an official capacity."

Fox denied that Werritty had accompanied him on official overseas visits. "Mr Werritty is not an employee of the Ministry of Defence and has, therefore, not travelled with me on any official overseas visits," Fox said in response to questions from John Mann, MP for Bassetlaw.

Werritty arranged talks between Fox and the MoD's private equity partner Porton Capital over a multimillion-pound legal battle between the MoD and US Post-it note maker 3M.

Hours after the meeting, which was not attended by officials and at which no notes were taken, Harvey Boulter, chief executive of Porton Capital, emailed 3M looking for a payment of $30m (£18m) to settle a dispute over the sale of a potentially lifesaving treatment to the US company and mentioning the award of a knighthood to 3M's British-born chief executive, Sir George Buckley.

The email said: "As a result of my meeting [with Liam Fox] you ought to understand that David Cameron's cabinet might very shortly be discussing the rather embarrassing situation of George's knighthood ... At a headline of $30m+ you will allow the MoD to internally save face." [See footnote.]

3M is now suing Porton Capital and Boulter personally for "blackmail", raising the prospect of Fox being summoned to give evidence at a trial in the US.

Werritty was one of a team of advisers, both official and otherwise, who travelled with Fox on holiday to Spain this summer.

Dugher said: "Fox has serious questions to answer about this. The defence secretary is privy to the most serious and sensitive information. You can't have old friends going around Westminster with the portcullis on their business cards claiming to be your adviser."

Dugher, who once worked as a special advisor in the MoD, said it was "most irregular" for a defence minister to have so many unofficial meetings at MoD headquarters. He raised concerns that meetings between Fox and Werritty would not have been recorded or minuted by officials.

"There are strict rules governing the conduct of ministers and advisers. This issue will not go away until Fox explains exactly what the status of the relationship between himself and Mr Werritty. Is Mr Werritty an adviser to Dr Fox or not? If he is, on what basis?"

Jones, who worked in the MoD's headquarters as armed forces minister from 2008 until last year, says he was shocked that a civilian with no security clearance was able to visit the MoD's heavily secured building so regularly.

"Having 14 meetings in 16 months is extraordinary. This is more than a friend visiting occasionally – this is once a month more or less. There is a clear pattern here and it raises further questions about what exactly is going on between Fox and Werritty."

He said it was "very concerning" that Werritty had been allowed to "present himself as an adviser in meetings with officials and politicians".

"There is a threat to national security if he's been attending meetings when classified information has been discussed," he said. "We don't know what they talked about because there are no records of the meetings.

"Fox needs to come clean about what his relationship is and why he is visiting so often."

"Having been a minister, I know that there are very clear rules about access to the main building. [One] is not allowed friends in the office – you have to book meetings in through the office. I once had a researcher who wasn't allowed into the building.

"As an MoD minister, you get to know a lot of things that only ministers and special advisors have been cleared for."

Fox and Werritty are also linked by a rightwing charity that Fox set up, and Werritty ran. The charity, called The Atlantic Bridge, was suspended last year following a Charity Commission investigation.

The charity, which had close links to neocons in America, is largely funded by billionaire hedge fund manager Michael Hintze. A trust set up by Hintze, the boss of CQS and the world's 880th most wealthy person, has donated £51,000 to The Atlantic Bridge.

The register of members' interests shows that Fox travelled on Hintze's private yet from Washington to the UK earlier this year, after giving a speech at an event to celebrate what would have been former US President Ronald Reagan's 100th birthday.

Werritty was a guest at Fox's 50th birthday party at his official residence in Whitehall last month.

• This article was amended on 14 October 2011 to append the following clarification: In the story above, reporting the background to a legal dispute between an investment company, Porton Capital and US conglomerate, 3m, we quote an email from Harvey Boulter, Porton's chief executive, to William Brewer, a lawyer acting for 3m: "As a result of my meeting [with Liam Fox, the defence secretary] you ought to understand that David Cameron's cabinet might very shortly be discussing the rather embarrassing situation of George [Buckley]'s knighthood". Boulter has contacted us and asked us to state that the meeting at which Buckley's knighthood was discussed was not the one with Fox but was at another meeting he had that day connected to the dispute.