“You have done a superb job in the 17 months since the election, and as shadow defense secretary before that,” Mr. Cameron said, calling Mr. Fox’s tenure a time of “fundamental changes in the Ministry of Defense and in our armed forces” as they modernized.

“On Libya, you played a key role in the campaign to stop people being massacred by the Qaddafi regime and instead win their freedom,” he said, adding, “I appreciate your commitment to the work of this government, particularly highlighting the need to tackle the deficit, and the relationship between Britain’s economic strength and our national security.”

Mr. Werritty has at no time held any official position on the Defense Ministry staff or in Mr. Fox’s personal office. In Mr. Fox’s public statements before his resignation, he said that the relationship was a personal one and that he had rebuked Mr. Werritty for using business cards carrying the House of Commons logo that identified him as an “adviser” to Mr. Fox. Mr. Fox also said that Mr. Werritty’s income did not depend on any “transactional” activity during the foreign trips they made together or in contacts with those Mr. Werritty introduced to Mr. Fox in his role as a self-styled defense consultant.

In recent days, articles in major British newspapers have suggested that the two men may have had an intimate relationship, and reporters have asked Mr. Fox, 50, whether it was sexual. Mr. Fox has answered obliquely, while other Conservative politicians have said that he is happily married to his wife, Jesme. On Monday, he used a 75-minute confrontation with opposition Labour politicians in the Commons to denounce the “innuendo” and “undermining” he said he had endured.

After an initial inquiry by a senior Defense Ministry official concluded last weekend that there was no evidence of any security breach, Mr. Cameron deferred any decision on Mr. Fox pending the conclusion of the O’Donnell inquiry. But the torrent of damaging headlines continued to build, even as Mr. Fox went to Paris on Thursday to meet with his French counterpart.

On Friday, Mr. Fox returned to a report in The Times of London that a not-for-profit company established by Mr. Werritty, Pagav Ltd., had received payments of about $230,000 from people with interests in promoting closer British ties with Israel, the United States and Sri Lanka. The newspaper said that some of the money was used by Mr. Werritty to pay for his overseas journeys with Mr. Fox.