LONDON: British Prime Minister Gordon Brown was under fresh pressure Monday after an anti-bullying charity said his staff had contacted them amid allegations about the leader's volcanic temper.

Christine Pratt, chief executive of the National Bullying Helpline, said that there had been three or four contacts made by Downing Street staff in recent years.

"What we are saying is staff in his office working directly with him have issues and have concerns and have contacted our helpline," she told the BBC.

The anti-bullying chief said she decided to go public with her concerns after being angered by ministers leaping to defend Brown over book extracts published Sunday claiming the prime minister terrified staff with his temper.

The new book by political journalist Andrew Rawnsley claims Brown grabbed one staff member by the jacket lapels and shouted at him, punched the back of a car seat after receiving bad news and repeatedly swore at advisors.

Brown is also accused of having "turfed a (secretary) out of her chair and (taken) over the keyboard himself" because she was "not typing fast enough", while a seat in his official car was allegedly "flecked with black marks" where he stabbed it with his pen in frustration.

The atmosphere at Downing Street got so bad that the head of the Civil Service, Gus O'Donnell, gave Brown a "pep talk", telling him: "This is no way to get things done," according to extracts in the Observer newspaper.

Downing Street labelled the allegations "malicious" and "totally without foundation", while Brown said any anger was directed at himself.

Colleagues rallied to support Brown, whose Labour Party is lagging David Cameron's main opposition Conservatives in opinion polls as a general election -- possibly in early May -- looms.

Business Secretary Peter Mandelson, was at the forefront of the defence, saying the picture painted by Rawnsley was "not one I recognise".

"I don't think he so much bullies people as is very demanding of people, he's demanding of himself," Mandelson told BBC television.

"There's a degree of impatience about the man but what would you like, some kind of shrinking violet at the helm of the government?"

His comments angered Pratt, however, who believes ministers attempts to deny there is anything wrong could worsen the stress of the staff involved.

"We believe that the present statement that Mandelson and others are putting out categorically denying that it is occurring is a nonsense and is non-credible," she said.

"To deny it, is going compound the stress of those who believe they are being bullied," she said, while stressing that the accusations against Brown did not amount to a guilty verdict.

"We are not saying that Gordon Brown is a bully," added Pratt.

Downing Street said the National Bullying Helpline had never contacted them about the allegations, adding there were "rigorous, well established procedures in place" to address the concerns of staff.

The revelations came the day after Brown launched what party officials called "Operation Fightback" ahead of a general election.

Even though the ballot has yet to be formally called, unofficial electioneering is already under way. The vote must be held by June 3 at the latest.

The book extracts told how the prime minister lost his temper in his official car once and "the aide sitting next to Brown... cowered because he feared 'that the prime minister was about to hit him in the face'."

O'Donnell launched his own investigations and felt the need "to calm down frightened duty clerks, badly treated phone operators and other bruised staff," according to the Observer.

A spokesman for the Cabinet Office said: "It is categorically not the case that the cabinet secretary asked for an investigation of the PM's treatment of Number 10 staff."