David Cameron is being called on to "urgently" review evidence around Chief Whip Andrew Mitchell's alleged foul-mouthed outburst at Downing Street police officers.
The Prime Minister was told by Labour to "get to the truth".
Mr Cameron was also told to take responsibility for the Tory enforcer's behaviour by the widow of murdered police officer Sharon Beshenivsky.
Police have suggested Mr Mitchell was close to being arrested after allegedly shouting "learn your f*****g place" and calling officers "plebs" when he was stopped from cycling out of Downing Street's main gates.
Although the former shadow police minister has apologised for not treating officers with due respect, he has denied using some of the language reported.
Conservative Nick de Bois warned that Mr Mitchell was in "deep trouble" if evidence emerged supporting the officers' version of events.
Labour called on the PM to take swift action to uncover the truth about the tirade, including examining Downing Street CCTV footage.
Shadow police minister David Hanson said: "The Prime Minister needs to review urgently Andrew Mitchell's version of events versus what the police officers have said.
"I'm asking for the PM to look at it, talk to Andrew Mitchell, clarify what he said. There will be clear evidence available, CCTV evidence, that could establish the truth."
John Tully, chairman of the Metropolitan Police Federation, said there was a written account of the incident in the notebooks of the officers from the Scotland Yard Diplomatic Protection Group, known as SO6.