Downing Street has backed Andrew Mitchell after he denied calling police "plebs" despite the chairman of the Metropolitan Police Federation warning the Tory MP had impugned "the integrity" of officers.
John Tully said David Cameron should hold an investigation after Mitchell denied calling a police officers plebs, but admitted he had not shown the police the "amount of respect I should have done" in an outburst last week.
"Clearly Mitchell is denying using certain words, effectively now impugning the integrity of the police officers," Tulley told Sky News.
The MP outside the Downing Street gate where the incident is said to have occured
"I think that is very serious. I think the Prime Minister or Downing Street officials should hold an inquiry and if Mr Mitchell is proved to have lied, then he should be sacked."
Asked if he called the officer a "pleb", Mitchell said on Monday morning: "I want to make it absolutely clear that I did not use the words attributed to me."
Despite the controversy, and four days of headlines about the altercation, the prime minister's spokesperson reportedly told reporters on Monday David Cameron "obviously accepts his [Mitchell's] statement."
He said the prime minister believes that Mitchell had done the right thing in apologising, and thinks a line should now be drawn under the affair.
Speaking earlier Mitchell earlier attempted to draw a line under the incident. But the Chief Whip refused to be drawn on what he actually said to the officer as he was questioned by reporters outside Whitehall on Monday.
"I have apologised to the police, I have apologised to the police officer involved on the gate and he's accepted my apology and I hope very much that we can draw a line under it there," he said.
Mitchell was reported by The Sun to also have called the police "morons" as well as "plebs" after they stopped him from leaving a Downing Street gate with his bike.
"Best you learn your f****** place. You don't run this f****** Government. You're f****** plebs," it reported him as saying.
Mitchell said on Monday that he had clashed with the police at "the end of a long and extremely frustrating day."
"I didn't show the police the amount of respect I should have done. We should all respect the police, they do an incredibly difficult job," he added.
"I apologised to the police officer involved and he has accepted my apology," he said.
His statement came as it emerged published records made by members of Scotland Yard's specialist protection team, which have been seen by The Sun newspaper, contradict the Tory enforcer's statement about the tirade he launched when he was stopped from cycling out of the main gates near No 10.
Labour has asked Downing Street's most senior civil servant to investigate the incident, claiming Mitchell's account of the row was "unravelling by the day".
The record is backed up by verbatim notes of the exchange made in the pocket books of two other officers, it said.
"The officers involved would have been happy to let the matter lie once Mitchell apologised," a source told the newspaper.
"But their integrity is now being called into question by Mitchell's denials and that is totally unacceptable.
Earlier on Monday former Tory minister Michael Portillo told ITV's Daybreak the word "pleb" was "very damaging."
"The word pleb I think is fundamental. That is, if it was said, that would be the very damaging word because that would tend to reinforce the impression ofthe Conservatives in the coalition as being aristocrats who don’t have social experience," he said.
Later Mr Clegg, interviewed by BBC Radio 4's Today programme from the Liberal Democrat conference in Brighton, said: "He challenges the way some of the words have been attributed to him.
"I am not going to give a running textual analysis but I think the fact that Andrew Mitchell has been as clear as he has that he is contrite about this, that he knows what he did was wrong, that he has apologised and the police officer in return has accepted the apology is important."
Asked if it was time to "move on", he said: "I cannot give a running commentary on what was and was not said in an incident where I was not there."