A police officer has been accused of masquerading as a member of the public and lying to help force the resignation of Britain's Chief Whip.
It emerged that a man whose testimony was crucial to the resignation of Andrew Mitchell as Government Chief Whip did not witness his outburst.
The "witness" was in fact a serving police officer who was nowhere near Downing Street at the time Mitchell was accused of calling police officers "f****** plebs", Channel 4 News suggests.
CCTV footage of the event released by Mitchell also appears to contradict police logs which stated there were "several members of the public present" at the time. It only shows one member of the public outside the gates - and no one who would match the description of the officer.
The claims emerged after a member of the diplomatic protection squad was arrested on suspicion of misconduct in a public office by police investigating the leaking of information relating to the altercation.
Government sources expressed deep concern over the suggestions there might have been a co-ordinated effort by police to discredit Mitchell.
Attention will focus on the Police Federation, which represents rank and file officers, and whose campaign against Mitchell was instrumental in leading to his resignation.
The "witness" is understood to have contacted his local MP John Randall, who was then Mitchell's deputy in the Tory whips' office, and claimed to have been passing by the gates of Downing Street with his nephew when Mitchell's altercation with officers took place. He told Randall he had watched on in "horror" as Mitchell "shouted obscenities" at police.
The account appeared to corroborate the police version of events, that Mitchell had called the officers "f****** plebs" when they stopped him cycling through the main gates.
Mitchell decided to resign his post around a month later.
The Dispatches investigation established the supposedly independent witness was in fact a serving police officer.
When the man was contacted by Dispatches he denied he was even there, saying: "I wasn't a witness to anything."
Mitchell, who has always claimed he never used the word "pleb" to describe the officer, admitted swearing but has always insisted parts of a police log published in the media were "false".
The Independent Police Complaints Commission said it had received a referral from the Met and would supervise the investigation.