Former Defence Secretary Liam Fox has attacked a "vindictiveness, even hatred" in his treatment by the media.

He told MPs he should have been "more willing" to listen to concerns raised about his links with Adam Werritty.

And he apologised to MPs for breaching the ministerial code. But Mr Fox, who resigned on Friday, said the "media frenzy... should worry all of us".

Meanwhile Parliamentary Standards Commissioner John Lyon is to launch an investigation into Mr Fox.

His office confirmed an investigation would take place, following a complaint from the Labour MP John Mann.

In his Commons statement on Wednesday, Mr Fox said: "I accept that it's not only the substance but perception that matters, and that is why I chose to resign.

"I accept the consequences for me without bitterness or rancour. I do not blame anyone else and I believe that you do not turn your back on your friends or family in times of trouble.

"It is, however, unacceptable that family and friends who have nothing to do with the central issues should be hounded and intimidated by elements of the media, including in this case elderly relatives and children.

ANALYSIS If anyone was expecting Liam Fox to grovel, then they'll be disappointed. Yes he said sorry more than once during his six minute statement, but there was a defiant, even angry tone to some of his words. Choosing to juxtapose his experience in Libya, meeting a man whose children had died, with his resignation two days later, he appeared to say: this has all been blown out of proportion, and I'm the only person who realises that. He also clearly believes he's been treated more harshly than others would have been in a similar situation - talking of a "personal vindictiveness" and "even hatred" in some of the coverage - clear references to the speculation about his sexuality. He's probably saved a fortune on thank you notes, given that he reeled off name after name of those who'd supported him in the past two weeks. Full support for the government was pledged, but the overall impression was that this was not a man who planned to subside quietly into years of lethargy and somnambulance on the backbenches. Liam Fox's statement to MPs In full: O'Donnell report on Fox Q&A: Liam Fox row

"It is difficult to operate in the modern environment, as we know, where every bit of information, however irrelevant and immaterial, is sensationalised and where opinions or even accusations are treated as fact."

He added: "Last week's media frenzy was not unprecedented, and it happens where a necessary free press and politics collide but I believe there was from some quarters a personal vindictiveness, even hatred, that should worry all of us."

A report by Cabinet Secretary Sir Gus O'Donnell, published on Tuesday, said Mr Fox had been warned about his working relationship with Mr Werritty by both his private office and permanent secretary but decided it was acceptable and should continue.

Speaking earlier on behalf of the government, Sir George Young, Leader of the House, told the Commons the permanent secretary should have taken her concerns further.

He said permanent secretaries would be given fresh advice on how to manage any similar situation in the future, and added that more generally, the rules surrounding access to ministers by lobbyists and other acquaintances would be tightened up.

Sir George also said it was clear that "the frequency, range and extent" of the meetings between Mr Fox and Mr Werritty "were not regulated as well as they should have been".

For Labour, shadow leader of the House Angela Eagle criticised Prime Minister David Cameron for failing to give the statement on Mr Fox himself.

'Optional extra'

She said Sir Gus's report was inadequate and left many unanswered questions, including whether Mr Werritty benefited financially from his access to the defence secretary, and whether Mr Fox authorised the payment of his friend's travel expenses by a number of wealthy backers.

She added: "Why was the defence secretary allowed to treat the ministerial code as if it were an optional extra?"

If there was anxiety about it, what action was taken Bernard Jenkin, Public Administration Committee

Labour want the government to publish details of all the meetings Mr Werritty had with ministers outside of the Ministry of Defence and are pressing the prime minister to say what he knew about Mr Werritty's business activities.

The Public Administration Select Committee has announced an inquiry into the role of the head of the civil service, which will also look at the service's actions in relation to Mr Werritty.

Speaking to BBC Radio 4's World at One, Conservative chairman Bernard Jenkin, said: "Why did it take more than 12 months before this issue came to a head, given that the private office must have known that Mr Werritty was popping up everywhere and knew about Mr Fox's movements?

"If there was anxiety about it, what action was taken, and if Mr Fox batted it away, why wasn't something done about it at that stage?"

He added: "There need to be clearer boundaries, so that when civil servants feel that those boundaries are being crossed, they have confidence to act independently of ministerial instructions and hold ministers to account."

Mr Fox resigned from the government on Friday, saying he had allowed his personal loyalties and professional responsibilities to become "blurred" over his dealings with Mr Werritty, his former flatmate and self-styled adviser.

The report said there had been a "clear breach" of the ministerial code on conflicts of interest but the former defence secretary did not benefit financially nor was national security compromised.

Despite having no role in the government nor the Conservative Party, Mr Werritty met with Mr Fox on 18 overseas trips, attended a number of important meetings with him, and had carried cards describing himself as his adviser.

The report found Mr Werritty had had "inappropriate" access to Mr Fox's diary - posing a "degree of security risk" to Mr Fox and any officials accompanying him.

It also concluded that the former cabinet minister should have declared to officials that donors who had provided funding to him when the Conservatives had been in opposition also gave money to Mr Werritty's firm Pargav.