Cameron allowed him to resign even after No 10 officials noted that CCTV ... - The Guardian

David Cameron left Andrew Mitchell "swinging in the wind" when he allowed his political career to come to an end knowing that a police account of a confrontation with armed officers was open to question, according to friends of the former chief whip.

Friends of Mitchell said it was "bloody astonishing" that Cameron had allowed him to resign even after No 10 officials had suggested that CCTV footage raised concerns about accounts of the 19 September incident. Mitchell met the prime minister to discuss the matter on Monday.

"The prime minister clearly decided not to raise concerns with [the Metropolitan police commissioner] Bernard Hogan-Howe," the source told the Guardian. "It is bloody astonishing. The approach was to leave this swinging in the wind rather than raise questions with the police."

Mitchell did not see the CCTV footage until after he had resigned from the government on 19 October. At the end of October, he was allowed to see the footage with his wife Sharon, his political ally David Davis and his lawyer.

Downing Street only agreed to hand over copies of the tapes to Mitchell on 10 December, allowing them to be broadcast on Channel 4. Officials had initially said the tape could not be shown publicly on the grounds of national security. This was successfully challenged by the Mitchell camp.

The timing of Mitchell's first viewing of the footage in October is crucial as it explains why he was unable to give a complete account of the incident in Downing Street at the time of his resignation. His camp say that senior officials in Downing Street – but not Mitchell – were allowed to see the footage while he was fighting to clear his name in government.

The row over the CCTV footage comes as the Mitchell camp moved to dismiss suggestions that the former chief whip had lost confidence in Hogan-Howe. The Times reported that Mitchell had expressed "no confidence" in Hogan-Howe after the commissioner said earlier this week that "nothing" caused him to doubt the account of the incident by two armed officers.

David Davis, the former shadow home secretary who is leading the campaign to clear Mitchell's name, told the Guardian: "Bernard Hogan-Howe is a very good cop who is the right man for the Met. As a good cop he is loyal to his people. But that makes it difficult for him to oversee anything involving a judgment over whether rules were broken."

Mitchell is understood to be pleased that the investigation into the police handling of the incident, dubbed Operation Alice, is being conducted by Pat Gallan, a deputy assistant commissioner. Mitchell was impressed by Gallan when they met.

There were tensions between the Mitchell camp and Hogan-Howe in the autumn when the commissioner refused to release a copy of the official police log of the incident in Downing Street on 19 September. All sides agree the chief whip lost his cool and swore when the officers declined to allow him to wheel his bike through the security gates.

But the officers claimed that Mitchell described them as "fucking plebs". They also claimed that "several members of the public" witnessed the encounter.

These claims were identical to the description of the incident by an off-duty police officer who claimed to have witnessed the incident. In an email on the evening of 20 September to his local MP John Randall, who was Mitchell's deputy in the whips' office, the officer claimed that "several other tourists" witnessed the incident in which Mitchell described police as "you fucking plebes [sic]". The CCTV footage, passed to Mitchell by Downing Street after a row over national security, appears to show that only one member of the public was standing by the gates at the time of the incident.

The officer has since admitted that he was not present during the incident. A 52-year-old man was arrested on Saturday night on suspicion of encouraging or assisting the commission of an act of misconduct in public office.

The Mitchell camp turned on No 10 after it emerged that the prime minister knew that Sir Jeremy Heywood, the cabinet secretary, had concluded that the account of the incident in the email was not consistent with the CCTV footage. At the time nobody in No 10 knew that the email had been sent by a serving police officer.

Downing Street confirmed on Wednesday this week that Heywood knew about the police log when it said that he declined to review it on the basis that it was a matter for the police. The Telegraph published the police log on the evening of 24 September, four days after the email was sent.

Asked why Heywood had not reviewed the police log, the prime minister's spokesman said: "Questions around the police log are part of the investigation that is currently going on."

The spokesman also confirmed that Cameron was "party to Sir Jeremy's review". The Mitchell camp says the prime minister would have known that the police log contained the same information which prompted Heywood to say that the email was inconsistent with the CCTV footage.

A friend of Mitchell said: "Back in September Downing Street had three quarters of the facts that are now in the public domain. The key fact is there were plain falsehoods in both the documents. This should have flagged up red flags in No 10. It is inexplicable that no questions were asked of the police."

One friend of Mitchell said Cameron had made a simple political calculation that the only way to save Mitchell's career was to accuse the police of lying. That was regarded as politically impossible.

Sources in No 10 said the prime minister agreed to the meeting in Downing Street on Monday night this week after Mitchell advised aides that the official police log of the incident and an email by a serving officer would be challenged by the CCTV footage.

Cameron, who watched the Dispatches/Channel 4 News investigation which raised questions about the police account, said Mitchell was calm in their meeting. "He was very calm and rational, but feels obviously disturbed by what seems to have happened and is very keen to get to the bottom of it."

The prime minister reached out to Mitchell by saying he had wanted him to stay in government. "Obviously I was wanting to keep him in his job. He made the apology which was right and necessary for what he himself admitted to saying in front of a police officer. But obviously he made an apology and I thought he should continue. It became impossible for him to do the job, and that's why he resigned and I accepted his resignation as you know."

Government sources said it was important to remember that nobody knew at the time that the email had been sent by a serving police officer. They also said that the email, the police log and the CCTV were reviewed within days of the incident. Key figures in No 10, though not the prime minister, reviewed these three key pieces of evidence at the time. Mitchell resigned nearly a month later.

• This story was amended on 21st December 2012. It originally reported government sources as saying that Andrew Mitchell had viewed CCTV footage of the incident while he was still in government. That was not correct and has been amended.