The Conservatives demanded an inquiry on Monday into allegations that Gordon Brown intimidated staff, claims which have brought bad publicity for the prime minister weeks before an election.
Mr. Brown has rejected as baseless and malicious allegations published in a Sunday newspaper that he had terrified staff by shouting abuse at them and in some cases had physically intimidated them. The claims came from extracts from a book by a political journalist.
They have overshadowed a Labour poll recovery which has seen the ruling party, in power since 1997, narrow the gap on the Conservatives to six points - a margin that could lead to a hung parliament in which no party has an absolute majority.
The head of a charity set up to counter workplace bullying said there had been "two or more" calls to its helpline from the prime minister's office but said she was not accusing Mr. Brown of being a bully. She did not say when the complaints were made.
"We would have hoped that Gordon Brown would have said that he was looking into this, that due process was being followed and that he takes these issues seriously," Christine Pratt, who runs the National Bullying Helpline, told BBC Radio 4.
With an election to be held by June, the claims inevitably sharpened the focus on Mr. Brown's character as a leader and provoked a political mud fight.
"They are very serious matters and I'm sure that Number 10 Downing Street and the civil service in some way will want to have some sort of inquiry to try and get to the bottom of what has happened here," Conservative leader David Cameron told reporters.
Business Secretary Peter Mandelson said the prime minister appeared to be the victim of a political campaign and dismissed calls for an inquiry.
"Do you not think we have better things to do than to chase up every rag, tag and bobtail rumour, innuendo and smear that anyone with a book to sell chooses to pump into the ether" Mr. Mandelson said at a conference in London.
"We've got a country to run, that's what's important to us. Nobody bullies, nobody tolerates bullying in this government, in any part of this government, period, zero, and that's it, OK?"
Mr. Brown, 59, replaced Tony Blair in mid-term in 2007 after serving as his finance minister for a decade. Mr. Brown is often portrayed as intense and brooding and critics, some within his own party, say he is an electoral liability.
He has recently opened up more in interviews, showing a more emotional side when discussing the death of his new-born daughter in a television chat show a week ago.