Chief Whip Andrew Mitchell “should explain fully and in detail his version of events” over the row with police at Downing Street, Nick Clegg said on Monday.
The deputy prime minister's comments come after 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.
Senior Coalition figures had called for a line to be drawn under the incident after the Sutton Coldfield MP apologised to the officer involved, but the documents will fuel speculation over his future in government.
The MP outside the Downing Street gate where the incident is said to have occured
It comes after Labour asked Downing Street's most senior civil servant to investigate the incident claiming Mr Mitchell's account of the row was "unravelling by the day".
Police reports, made for senior officers, detail how the Tory was warned he would be arrested under the Public Order Act if he swore at the team again, according to The Sun.
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.
"Perhaps with the full verbatim report in the public domain, people can make up their own minds."
When allegations about the tirade were published on Friday, Mr Mitchell issued a statement denying using "any of the words that have been reported".
But it was claimed yesterday that while he remains adamant he did not use the word "pleb", he did swear.
The officer who bore the brunt of the former shadow police minister's rant made a note within hours of the exchange after the Tory said "You haven't heard the last of this", The Sun claimed.
Shadow home secretary Yvette Cooper wrote to Cabinet Secretary Sir Jeremy Heywood asking for Mr Mitchell and the officers involved to be interviewed, statements to be reviewed and an examination of CCTV footage.
A swift investigation would allow Prime Minister David Cameron to "decide on the Chief Whip's continued position" based on the facts, she added.
"Given the justified anger and concern from police officers of all ranks, Mr Mitchell should apologise publicly immediately," she said.
"But Downing Street also need to make sure there is now a proper investigation by the Cabinet Secretary into this incident and release in full what was said.
"Andrew Mitchell's account of what went on is unravelling day by day and we need to know exactly what happened.
"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," she added.
"From the reports we have seen it appears that either the Chief Whip used very offensive language to dismiss an officer on duty and has not told the public the full story.
"Or, alternatively, Mr Mitchell and the Prime Minister are saying the testimony of police officers who protect Downing Street cannot be trusted or should be ignored.
"Either of those alternatives are extremely serious, which is why this needs to be fully investigated. David Cameron cannot dismiss this incident and hope it goes away."
Deputy Prime Minister Nick Clegg said the Tory had been "wrong" to lose his temper but suggested if no new revelations emerged about the confrontation Mr Mitchell should be able to remain in his post.
Tory Communities Secretary Eric Pickles described his colleague's behaviour as "ungallant" but should not be sacked for a "bad temper".
Mr Mitchell, a keen cyclist, was reported by The Sun to also have called the police "morons".
"Best you learn your f****** place. You don't run this f****** Government. You're f****** plebs," it reported him as saying.
In a statement on Friday the Tory, who was also a minister under John Major in the early 1990s, said: "On Wednesday night I attempted to leave Downing Street via the main gate, something I have been allowed to do many times before.
"I was told that I was not allowed to leave that way. While I do not accept that I used any of the words that have been reported, I accept I did not treat the police with the respect they deserve.
"I have seen the supervising sergeant and apologised, and will also apologise to the police officer involved."
Downing Street declined to comment.