Defence Secretary Liam Fox disclosed today that he had met his friend and former flatmate Adam Werritty during around 18 overseas visits.
In a Commons statement, Dr Fox also disclosed that Mr Werritty had visited him 22 times at the Ministry of Defence in the past 16 months - more than previously acknowledged.
He said he was now putting in place measures to ensure Mr Werritty did not make private visits to the MoD in future, will not attend international conferences where he is present and they will not meet socially abroad when Dr Fox is on official business.
Dr Fox said he had first met Mr Werritty in 1998 and that he had worked as a paid intern in his House of Commons office while the Conservatives were in opposition.
In addition he said that he had paid Mr Werritty £5,800 for research work that he did for him in opposition.
He said that the majority of his meetings with Mr Werritty in the MoD had been "short social meetings" and that in only four instances were other people present.
It was at one of those meetings in June that Dr Fox said he first learned that Mr Werritty was using a business card stating that he was his advisor - a practice he told him to stop.
"Mr Werritty was never present at regular departmental meetings, during private meetings we did not discuss either commercial or defence matters, he had no access to classified documents, nor was he briefed on classified matters," Dr Fox said.
"I accept with the benefit of hindsight that I should have taken greater care to ensure a more transparent separation of government, party political, and private business and that meetings were properly recorded to protect myself and government from any suggestion of wrongdoing.
"I accept my personal responsibility for this."
Dr Fox confirmed that Mr Werritty had arranged a meeting between him and Harry Boulter, the chief executive of the Porton Capital investment fund, while he was in Dubai last June.
He said that Mr Boulter had initially requested a meeting in April - a request which he renewed when he met Mr Werritty by chance in Dubai.
"During the week of the 13th June, Mr Werritty was dining in Dubai at a nearby table and Mr Boulter again requested a meeting and Mr Werritty suggested it might be possible the following day as I was coming through on my return from visiting forces in Afghanistan," he said.
Dr Fox said they had had a "general discussion" about what Cellcrypt - one of Porton's companies - might be able to do for the MoD. At the end of the meeting Mr Boulter "in the interests of probity" mentioned he was in a dispute with the US conglomerate 3M alongside the MoD.
Dr Fox said Mr Boulter had then sent emails claiming he had had a discussion on the issue of the knighthood awarded to 3M's chief executive, Sir George Buckley, which subsequently became the subject of a blackmail case in the United states.
"I made it clear that I was willing to testify that I had never had any such discussions. Subsequently Porton Group has since clarified that Harvey Boulter had not discussed the matter of the knighthood," Dr Fox said.
"I accept that I should not have had a meeting with a potential commercial supplier without an official being present. This was entirely my fault and I take full responsibility for it."
Downing Street said that David Cameron had now seen the interim findings of a review carried out by MoD Permanent Secretary Ursula Brennan into Dr Fox's relationship with Mr Werritty.
"It is clear, as Liam Fox himself said yesterday, that serious mistakes were made in allowing the distinction between professional responsibilities and personal loyalties to be blurred - and this has clearly raised concerns about impropriety and potential conflicts of interest," a No 10 spokesman said
"While the Permanent Secretary's initial conclusion is that no classified or other defence related official information was discussed with or given to Mr Werritty by the Secretary of State or the department, it is clear that much tighter procedures are needed within the department to ensure that the Ministerial Code is properly adhered to in future.
"Following these interim findings the Prime Minister has asked the Cabinet Secretary to work with the Permanent Secretary to complete the report, addressing all the remaining questions that have been raised by this issue."
Labour backbencher John Mann later wrote to parliamentary standards commissioner John Lyon asking him to investigate Dr Fox.
He called for an examination of allegations that Dr Fox allowed Mr Werritty to live rent-free in and run a business from a taxpayer-funded property. Mr Werritty was also allowed to run the Atlantic Bridge organisation from Dr Fox's parliamentary office, according to Mr Mann.
The Bassetlaw MP said: "In my view Dr Fox has allowed his friend to financially gain from the privileges that he has had access because he is a Member of Parliament.
"There is no reason for Dr Fox to wait and see what happens. He should go now."