Opposition parties have demanded an inquiry into allegations of bullying in Downing Street.
The row over claims that the prime minister bullies those working for him threatened to get out of control today after Labour demanded proof of the allegations and the charity making them found itself facing serious criticism.
Liberal Democrat leader Nick Clegg said he thought an inquiry was appropriate.
"If [the allegations are] true they're pretty significant," he told the BBC.
"How you behave in politics when you're behind closed doors. I think it matters. No 10 needs to come clean."
David Cameron backed up that demand this morning.
"I'm sure that No 10 Downing Street and the civil service in some way will want to have some sort of inquiry to get to the bottom of what has happened here," the Tory leader said.
"One way for that to happen is for Sir Philip Mawer, who is in charge of policing the ministerial code, to be asked to look into this and to find out what has been happening and get to the bottom of it.
"To me, all of this just says we need to get on, have a general election and have a fresh start."
The dispute began yesterday, when the Observer began the serialisation of Andrew Rawnsley's new book, which claimed civil service head Sir Gus O'Donnell had to warn the prime minister about his behaviour towards staff.
The prime minister's spokesman instantly shot down the allegations, saying: "These malicious allegations are totally without foundation and have never been put to No 10."
Sir Gus finally said he had never had a conversation with the prime minister over his behaviour this afternoon.
The confirmation will be a relief to Downing Street, but many Westminster observers were left asking why the confirmation emerged so long after the story broke.
This morning a tidal wave of questions from journalists had the prime minister's spokesman on the back foot.
He said that Sir Gus had not been asked to conduct an official investigation, but refused to comment on whether or not he had given the prime minister a "verbal warning".
The row intensified after the National Bullying Helpline intervened in the dispute by saying it had been contacted by employees in Mr Brown's office.
The prime minister's spokesman has demanded proof of the allegations and pointed out none of the published allegations relate to Mr Brown.
"We have rigorous, well established procedures in place to allow any member of staff address any concerns over inappropriate treatment or behaviour," a Downing Street spokesman said yesterday evening.
Charity boss Christine Pratt was vague about exactly how many calls the helpline had received from No 10.
"Over recent months we have had several inquiries from staff within Gordon Brown's office," she told the BBC.
"Some have downloaded information; some have actually called our helpline directly and I have spoken to staff in his office.
"We are not suggesting that Gordon Brown is a bully, what we are saying is staff in his office working directly with him have issues, and have concerns, and have contacted our helpline."
Ms Pratt specified that no one had mentioned Mr Brown by name and her intervention threatened to damage her organisation as much as the government. She has not provided No 10 with any "email evidence" backing up her claims.
This morning, Prof Cary Cooper, an expert on workplace stress, quit as patron of the charity, describing the decision to go public as "wholly inappropriate".
TV presenter Sarah Cawood also stepped down as a patron, saying: "In the light of recent events, where confidential phone calls were made public, I have decided it is no longer a campaign with which I want to be associated."
Mr Rawnsley's book details alarming stories of the prime minister grabbing people by their lapels and shouting in their face. It also highlights behaviour that can only be described as paranoid.
But there was considerable support for the prime minister, with the business secretary and home secretary both defending his character.
First secretary Peter Mandelson said: "No one tolerates bullying in this government or in any part of this government. Period. Full stop. That's it.
"If you think we're going to spend our time chasing around newspapers that want a splash on their front pages, let me tell you: we've got better things to do with our lives."
Mr Mandelson went on to suggest that the controversy had taken on the "odour" of a political move, but the Tories were quick to dismiss any suggestion that the bullying charity is acting in their interests, despite the presence of Ann Widdecombe as one of its patrons.
Downing Street was happy to confirm that there are no complaints or grievances currently being dealt with by staff in No 10 or the government department to which it is attached, the Cabinet Office.
But Mr Brown's staff were reluctant to commit to definitively answering a query about whether there had been any such complaint made in the last three years.