The Metropolitan Police should be allowed to "get to the truth" about whether a serving officer fabricated evidence against Andrew Mitchell that contributed to his resignation from cabinet, David Cameron has said.
Speaking during prime minister’s questions on Wednesday, Cameron said Scotland Yard was conducting a "thorough and well resourced investigation to get to the truth of the matter as quickly as possible” under the supervision of the Independent Police Complaints Commission.
"Police officers posing as a member of a public and sending an email to blacken the name of a cabinet minister is a serious issue," he told MPs.
Mitchell walked into the Commons with his friend and ally, former Tory leadership contender David Davis, and spent the duration of the session stood at one end of the chamber chatting with other MPs.
The former chief whip carefully avoided any facial expressions as the prime minister addressed the issue of his resignation from cabinet.
Scotland Yard today vowed to "get to the truth" of allegations that a police officer falsely claimed to have witnessed the "plebgate" row that led to Mitchell being forced to quit as chief whip.
The officer is said to have written to his local MP, posing as a member of the public, giving details of the altercation that took place when the senior Tory attempted to cycle out of the main gates in Downing Street.
Number 10 said the claims - which emerged after a member of the diplomatic protection squad was arrested - were "exceptionally serious".
The Metropolitan Police Service said on Wednesday that “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. If any evidence emerges of conspiracy this will form part of the investigation.
"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."
It comes after CCTV footage of the incident was broadcast for the first time and appeared to contradict parts of a leaked police log about the spat.
Although there is no sound, the MP - who clung on to his job for a month before finally resigning - can be seen with his bicycle talking to three officers by the main gate for around 20 seconds. He then wheels it over to the side gate and exits.
The footage, broadcast by Channel 4 News, appears to show there were few members of the public passing by at the time, apparently contradicting police records.
Mitchell demanded a full probe into the police account of events and insisted the email - sent to MP John Randall - was key to the loss of his job.
"I always knew that the emails were false, although extremely convincing," he told Channel 4 News last night.
"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 police officer reportedly did not disclose his job in the email to Randall, who was Mitchell's deputy in the government whips' office and reportedly suggested he would quit unless his boss left his post.
He described how he had been walking past Downing Street with his nephew when the spat took place.
The email said Mitchell had sworn repeatedly and called the officers on guard "plebs". It also suggested that passers-by outside the gates had been shocked, and some may have filmed the confrontation.
The account closely matched that in the official police log, which was later leaked to the Daily Telegraph.
Mitchell said his first reaction to the story emerging in September was "there's not really much of an altercation.
"There were three phrases above all which were hung around my neck for the following 28 days every day in the press which were used to destroy my political career and were used to toxify the Conservative Party," he said.
"They are completely untrue, I never said phrases like that at all, I would never call someone a f****** pleb, anyone who knows me well would know that it is absolutely not in me to use phrases like that."
Asked why he did not give a more detailed account before, Mitchell said: "Well when the story broke, the decision was made that I would apologise for what I did say, and my apology was accepted, there was no police complaints and that we would let it lie.
"Now with the benefit of hindsight, that was clearly the wrong decision."
The Labour Party has said there needs to be a "full and independent investigation into what happened in Downing Street" on that day.