British Defence Secretary Liam Fox has apologised for a row over his friend's reported influence over government policy, but vowed to fight his case in parliament.
Fox said on Sunday he was "very sorry" for "giving the impression of wrongdoing".
In a statement he also accepted it was "a mistake to allow distinctions to be blurred between my professional responsibilities and my personal loyalties to a friend".
But the minister said he would answer "all questions" about friend Adam Werritty's involvement in government business, including Afghanistan and Libya, during the scheduled House of Commons defence questions on Monday.
Fox insisted that "at no stage" did he provide classified information or briefings to Werritty, or assist the businessman in his commercial endeavours.
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The under-fire minister also revealed he had apologised to Prime Minister David Cameron for meeting a commercial supplier without the presence of an official, and was working to legislate against such meetings in the future.
Fox stopped short of apologising for the nature of his relationship with Werritty, and regretted only that he "may have given the impression of wrongdoing" and "given third parties the misleading impression that Werritty was an official adviser".
Cameron on Saturday said that Fox had his "full confidence" despite the allegations about Werritty, who was best man at Fox's wedding but has no official government role.
But hours later Downing Street said Cameron wanted a preliminary report setting out the facts by Monday and was not prepared to wait until an internal Ministry of Defence (MoD) inquiry reports back in a fortnight.
Fox, who visited Libya on Saturday, ordered the MoD inquiry on Friday into claims that Werritty had privileged access to him despite having no official role or security clearance.
The row escalated on Saturday when The Observer newspaper carried footage on its website of Werritty apparently attending a meeting between Fox and Sri Lankan President Mahinda Rajapakse in London in 2010.
Other newspapers also reported that Werritty had brokered a meeting in Dubai in June between Fox and a company hoping to sell phone call encryption technology to the British military.
They discussed whether British troops in Afghanistan could use it to call home without being detected by the Taliban, the Financial Times said.
The Conservative MP argued the Dubai meeting came about by chance while he was on a stopover from Afghanistan but admitted that he met Werritty on an official visit to Sri Lanka in July, and that Werritty had visited him 14 times in 16 months at the MoD's London base.
Fox has consistently refuted claims that the friendship threatened national security, and an MoD spokesman said allegations of wrongdoing were "baseless".
However, the defence chief claimed on Sunday to "have learnt lessons" from the affair and said he would take greater care in the future to protect himself and the government from accusations of wrongdoing.
Labour MP Jim Murphy, the shadow defence minister, said on Sunday he had written to Cameron calling for a full investigation, highlighting "several shortcomings" in the current probes.
"The terms of reference are narrow and simply inadequate in light of the evidence that has come to light," he added.
"It is important that the breadth of this inquiry matches the severity of the accusations."
