Andrew Mitchell row: Minister 'swore in frustration'
The chief whip did swear during a confrontation in Downing Street - but not at police, sources say.
Andrew Mitchell had earlier apologised to police for failing to show officers "respect" after being prevented from cycling through the main gate last week - but he denies using the word "pleb".
The BBC has been told he swore in frustration at the situation.
Communities Secretary Eric Pickles said Mr Mitchell should not lose his job over the use of "inappropriate words".
Cabinet minister Ken Clarke has also defended Mr Mitchell, who he said was a reasonable and courteous man.
The row broke out on Wednesday after Mr Mitchell was told by officers to get off his bicycle as he left Downing Street and go through the smaller pedestrian gate.
Soon afterwards, the MP for Sutton Coldfield said he did not accept "that I used any of the words that have been reported" - but did not go into specific details.
Meanwhile, a friend of Mr Mitchell, quoted by the Sunday Telegraph, says the minister was frustrated by the row, and admits he "lost it a bit" but was "not accusing anyone of lying".
'Proud to be a pleb'
The friend added: "He realises there may be differing versions of what was said but he is adamant he did not use the words he is reported to have used."
Speaking on the BBC's Sunday Politics programme, Mr Pickles said he believed his cabinet colleague used "ungentlemanly" and "ungallant" language.
But he added: "I don't believe somebody should lose public office merely because they used inappropriate words and displayed a bad temper."
The communities secretary refused to say whether Mr Mitchell should resign if he used the word "pleb", but said "he has never used it in my presence, but I'm proud to be a pleb".
On Saturday, Mr Clarke, a minister without portfolio in the cabinet, said: "I have known Andrew for a long time and he is a perfectly reasonable, courteous man with the same high regard for the police services as anyone else.
"He obviously had a flare of bad temper on this occasion and has rightly apologised. I do think this should be allowed to set the matter at rest."
Yvette Cooper, shadow home secretary, has called for the government to release in full what Mr Mitchell said to the police officers and for an investigation into the incident.
In a letter to Cabinet Secretary Sir Jeremy Heywood, Ms Cooper wrote that Mr Mitchell's behaviour was "completely unacceptable" and that "a half-hearted private apology is clearly insufficient".
"Everyone is already deeply concerned that a senior cabinet minister is reported as dismissing police officers doing an important security job as 'plebs'," she wrote.
"It is really important that the prime minister does not compound this by dismissing the testimony of police officers and the evidence from their notebooks without proper investigation."
The Liberal Democrat president, Tim Farron, described Mr Mitchell's alleged outburst as "utterly, indeed beyond, unacceptable".
His party leader, Nick Clegg, told the BBC's Andrew Marr programme it was right for Mr Mitchell to apologise, but argued it was time to "draw a line under it" unless more information emerged about the incident.
"I think civility and being courteous to the police is important at all times, but it is especially important given the tragic events around the killing of PCs Fiona Bone and Nicola Hughes.
"What Andrew Mitchell did was wrong, very wrong. He knows that and has apologised to the police and explained himself," Mr Clegg said.
The row broke out after reports of the encounter emerged in the Sun on Thursday.