Britain's former defence minister Liam Fox caused a security risk by leaking details of future foreign trips to his close friend, an official report criticising his actions said Tuesday.

The highly anticipated report by the country's top civil servant found that Fox, who resigned on Friday after a week of intense pressure, had breached the ministerial code in his dealings with 34-year-old Adam Werrity.

Werritty posed as Fox's adviser despite having no government role and accompanied the minister on a string of overseas visits, with Werritty's travel being funded by backers linked to Israel and Sri Lanka.

"Dr Fox's actions clearly constitute a breach of the ministerial code which Dr Fox has already acknowledged. This was a failure of judgement on his part for which he has taken the ultimate responsibility in resigning," Cabinet Secretary Gus O'Donnell said in the report.

But civil service chief Gus O'Donnell said in the report that he had "found no evidence that Dr Fox gained financially in any way from this relationship".

Prime Minister David Cameron commissioned the report last week to get to the bottom of 50-year-old Fox's links to Werritty, who was the best man at the minister's wedding in 2005.

Cameron's spokesman said he accepted O'Donnell's recommendations for a tightening of the ministerial code, and for the rules governing government advisers.

The report said Fox, who played a key role in Britain's military campaigns in Libya and Afghanistan, was guilty of an "inappropriate blurring of lines between official and personal relationships".

It criticised Fox for sharing with Werritty the advance details of his trips abroad. The pair went on 18 foreign trips together after Fox took office in May 2010.

"The disclosure outside MOD (Ministry of Defence) of diary details about future visits overseas posed a degree of security risk not only to Dr Fox, but also to the accompanying official party," it said.

Werritty's use of business cards falsely portraying himself as an advisor to Fox "risked creating the impression that Mr Werritty spoke on behalf of the UK Government or was officially associated with Dr Fox".

The report also said it was "not appropriate" for Werritty to have attended a meeting between Fox and Matthew Gould, the incoming British ambassador to Israel, in September 2010, where they discussed "international defence and security matters".

Civil servants warned Fox of the risks of his association with Werritty but he ignored them, O'Donnell added.

The report also listed six individuals or groups that had contributed money to Pargav, a not-for-profit company set up by Werritty. The money helped to fund his travel abroad with Fox.

Fox said in a statement on Tuesday that he welcomed the fact that the report cleared him of having made any financial gain or having breached national security.

But he accepted that it was a "mistake" to blur distinctions between government and private roles.

The main opposition Labour party said the "superficial and narrow" inquiry left unanswered questions.

"This report only scratches the surface of potential wrongdoing. This is a murky business and it has not yet been resolved," Labour defence spokesman Jim Murphy said.

Conservative party lawmaker Fox stepped down amid reports that financial backers linked to Israel and a private security firm had funded Werritty's first-class travel and hotel stays during his time with the minister.

Fox admitted that Werritty had also visited him 22 times at the Ministry of Defence in London, in addition to the foreign trips.

Fox has been replaced by Philip Hammond, the former transport minister.

The government has promised to bring in new laws governing lobbyists in the wake of the case.