Scotland Yard today vowed to “get to the truth” behind allegations that one of their police officers masqueraded as a member of the public to “frame” the former Government Chief Whip Andrew Mitchell.
The officer is accused of writing to his local MP, posing as a passer-by, giving details of an altercation that took place when Mr Mitchell attempted to cycle out of the main gates in Downing Street.
However it emerged yesterday that the “witness” was in fact a serving police officer who was nowhere near Downing Street at the time Mr Mitchell was accused of calling police officers “f****** plebs”.
The incident has badly damaged trust between Downing Street and the police – which was already under pressure over police cuts and the forced resignation of the previous Met Commissioner Paul Stephenson.
A spokesman for David Cameron said the claims were “exceptionally serious” and called for an urgent investigation.
The Metropolitan Police Service said today it was conducting a “thorough and well-resourced” inquiry.
“The allegation that a serving police officer fabricated evidence is extremely serious. It goes to the very heart of the public's trust in the police service,” it said in a statement.
“The Metropolitan Police Service is conducting a thorough and well-resourced investigation to get to the truth of the matter as quickly as possible.”
The Met said that since opening the investigation an officer had been arrested on suspicion of misconduct in public office and the investigation has been referred to the Independent Police Complaints Commission for supervision.
“If any evidence emerges of conspiracy this will form part of the investigation,” it said.
“This is a fast-moving and comprehensive investigation and the highly unusual events of the last three days have shown this inquiry will need to go where the evidence takes us as it progresses."
Attention is likely focus on the Police Federation – which represents rank and file officers – and whose campaign against Mr Mitchell was instrumental in leading to his resignation. It has strongly denied any “conspiracy”.
CCTV footage of the event released by Mr Mitchell last night appears to contradict the police logs of the incident 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.
A Dispatches investigation for Channel 4 News disclosed that the police officer, posing as a member of the public, contacted his local MP John Randall – who was then Mr Mitchell's deputy in the Tory whips' office – and claimed to have been passing by the gates of Downing Street with his nephew when Mr Mitchell's altercation with officers took place.
He told Mr Randall he had been outside Downing Street hoping to catch a "glimpse of a famous politician" and watched on in "horror" as Mr Mitchell "shouted obscenities" at the police officers.
The account appeared to corroborate the police version of events, that Mr Mitchell had called the officers "f****** plebs" when they stopped him cycling through the main gates.
It emerged tonight that the email bearing a close resemblance to the details of the police log was written on September 20 - the day before The Sun first reported claims that Mr Mitchellcalled officers "plebs".
The email was published on the website of Channel 4 News, which drew on its false account of the then Cabinet minister's row with police in last night's report.
The email is littered with grammatical errors, spelling mistakes, inappropriate capitalisation and malapropisms, including a reference to Mr Mitchell's "digesting behaviour".
The writer says he recognised Mr Mitchell and "corrected" his nephew, who initially thought Mr Mitchell was mayor of London Boris Johnson.
"Imagine to our horror when we heard MR MITCHELL shout very loudly at the police officers guarding YOU (expletive blacked out) PLEBES !!" and "YOU THINK YOU RUN THE (expletive blacked out) COUNTRY" and just continued to shout obscenities at the poor police officers.
"My nephew, as was I, totally taken aback by his, MR MITCHELLS' behaviour and the gutter language he used, especially it appeared directed at the police officers.
"Now I know that the other people/tourists standing with us were also shocked and some were even, inadvertently filming the incident (it wouldn't surprise me that in this age it'll be on YouTube or other social media website.) One person even remarked as to why was BORIS swearing."
Mr Mitchell demanded a full probe into the police account of events and insisted the email was key to the loss of his job.
“I always knew that the emails were false, although extremely convincing,” he said. “It has shaken my lifelong support and confidence in the police. I believe now there should be a full inquiry so we can get to the bottom of this.”
The former Tory leader Lord Howard told BBC Radio 4's Today: “I am appalled at the suggestion that a police officer could do what it is alleged that the police officer in question did.
“And I certainly do hope that Andrew Mitchell is restored to government at the earliest possible opportunity.”
The former Conservative shadow home secretary David Davis said his party colleague had been the victim of “a really serious injustice” and should be restored to the ministerial ranks.
“This is a shocking revelation that a police officer seems to have masqueraded as a civilian - more than seems to, I've seen the emails and clearly did so - and acted in a way which effectively completely undermined Mr Mitchell in the eyes of the Prime Minister and the rest of Downing Street right at the point they were making the decision - what do we do, do we support him or not?” he told the BBC Radio 4 Today programme.
“As a result we have had a serious injustice, a really serious injustice. He should be returned to high office.
Mr Davis criticised the Cabinet Secretary and the Met for failing properly to examine the evidence when the allegations first emerged.
“Whether it's the Met investigation or Sir Jeremy Heywood, none of this is exactly Sherlock Holmes,” he said.
“All the investigations did not go to the heart. Look at the CCTV, see whether it is consistent with the allegations made, consistent with what's been said. It plainly wasn't.”