Downing Street today backed Justice Minister Jonathan Djanogly after it emerged he hired a firm of private detectives to carry out undercover investigations of his aides and colleagues.
The Prime Minister's spokesman conceded that the Tory MP may have "overreacted" after rumours appeared about him in the press, but said he still had David Cameron's "full confidence".
Mr Djanogly was forced to defend his actions after the Daily Telegraph obtained a copy of the report by Morris Chase International.
It showed the then-shadow solicitor general had instructed the firm to conduct "discreet inquiries under the pretext of writing a newspaper article" last year to establish the views of people including a former council leader.
The company said all the information was obtained legally and the Huntingdon MP insisted he would "never have contemplated condoning anything unlawful or dishonest".
But one of those targeted, Tory ex-leader of Huntingdon council Derek Holley, called on Mr Djanogly to "consider his position" in government.
"Quite frankly I was just appalled by it all," Mr Holley told BBC Radio 4's Today programme. "I have been in local politics and associated with national politics for 34 years, and I have never, ever experienced anything like this in the whole of that time."
In a statement Mr Djanogly said: "Following a series of malicious allegations made against me in newspapers last year, I felt I had to act to find out who was spreading these untrue stories.
"I instructed a firm of private investigators to try to find out the source of these stories because I was extremely upset that my private family life had been invaded.
"A report of their investigation was prepared and sent to me on a confidential basis and I am very disappointed to see the report released publicly without my consent.
"I would never have contemplated condoning anything unlawful or dishonest in the investigations, and the investigators have assured me that their inquiries were carried out in an entirely lawful manner.
"I am sorry if some people judge that I made a mistake. With hindsight I can see that I may have overreacted, but I was being subjected to very malicious, anonymous attacks on my family.
"I paid for the cost of the investigation myself and did not claim it back on parliamentary expenses."
Asked this morning if Mr Cameron had full confidence in Mr Djanogly, the Prime Minister's spokesman replied: "Yes."
"The PM will judge him on his performance as a minister," the spokesman said. "He has said himself that with hindsight he may have overreacted."
Michael Morris, a director of the firm, told The Telegraph: "All the information obtained for and reported to Mr Djanogly was developed legally. The use of pretext is legal as long as the requirements and principles of the Data Protection Act are adhered to."
The newspaper said the report cost Mr Djanogly, who is a solicitor and reputedly one of the richest members of the Commons, more than £5,000.
It was reported to show that election agent Sir Peter Brown resigned "over the expenses scandal" and not, as suggested at the time, ill health.
Another senior Tory is said to have told the undercover investigator: "Sir Peter was very upset and unhappy about being lied to. He knew Jonathan's cleaner was his au pair. We all knew her because she used to hand out drinks at constituency social events."
The report also contained information about an alleged "conspiracy" to undermine the MP.
"There does not appear to be any current activity among the conspirators to revive the expenses allegations," it concluded. "This is because they do not have the time or resources to conduct investigations to trace the au pairs.
"All four sources say that you have been damaged severely politically. Brown said, 'Jonathan has lived to die another day'."
News of Mr Djanogly's actions emerged just hours after Deputy Prime Minister Nick Clegg had condemned Labour's habit of chopping and changing its ministerial team.
In a speech, Mr Clegg accused the previous government of being driven by headlines, and added: "This Government recognises that constant reshuffling of the ministerial deck... is not conducive to good government, and that we will aspire to greater stability in the way ministers are allowed to govern."