Mitchell is owed an apology - PM
David Cameron said former Tory chief whip Andrew Mitchell was owed an apology as the row between police and politicians over the "plebgate" affair escalated.
The Independent Police Complaints Commission (IPCC) said Inspector Ken MacKaill, Detective Sergeant Stuart Hinton and Sergeant Chris Jones should have faced misconduct hearings for lying about what Mr Mitchell said in a private meeting about the row last year.
At Prime Minister's questions Mr Cameron said the conduct of the officers, who were representing the Police Federation, was "not acceptable".
He said Mr Mitchell was "owed an apology, the conduct of these officers was not acceptable" and "these things should be properly investigated".
The Prime Minister backed the stance taken by Home Secretary Theresa May, who has insisted West Mercia Police force was "quite wrong" not to take disciplinary action.
The force's chief constable, David Shaw, has been summoned to give evidence to the Home Affairs Select Committee on the issue next week .
The committee's chairman Keith Vaz raised the row with Mr Cameron in the Commons, saying the IPCC report was "damning".
Mr Cameron said: "I agree 100% with what the Home Secretary said yesterday and I think we should be clear about what we are discussing here.
"The whole case about what happened outside 10 Downing Street, that's with the CPS and we have to leave that on one side until they make their decision.
"What's being discussed here is the fact that ... the former chief whip had a meeting with Police Federation officers in his committee where he gave a full account of what had happened, they left that meeting and claimed he had given them no account at all.
"Fortunately this meeting was recorded so he has been able to prove that what he said was true and what the police officers said was untrue."
Mr Cameron added: "He is owed an apology, the conduct of these officers was not acceptable, these things should be properly investigated, as the Home Secretary has said."
It was right for Mr Vaz's committee to "discuss this with the chief constables concerned and try to get to the bottom of why better redress has not been given".
Mr Mitchell met Mr MacKaill, Det Sgt Hinton and Sgt Jones, federation representatives of West Mercia, Warwickshire and West Midlands respectively, on October 12 last year to "clear the air" following his clash with police in Downing Street.
A transcript shows Mr Mitchell apologised for swearing at the police officers but denied using the word "plebs".
In comments made after the meeting, Mr MacKaill claimed the former Tory chief whip would not provide an account of the incident.
West Mercia Police conducted an internal investigation into claims that the three officers were trying to discredit Mr Mitchell but concluded there was no case to answer for misconduct or gross misconduct.
IPCC deputy chairwoman Deborah Glass said she disagreed with their findings and added that the evidence reveals "an issue of honesty and integrity, not merely naive or poor professional judgment" among the federation representatives.
She said: "In the media and political climate of the day, I do not consider that the officers could have been in any doubt about the impact of their public statements on the pressure being brought on Mr Mitchell.
"As police officers, they had a responsibility to present a fair and accurate picture.
"Their motive seems plain: they were running a successful, high-profile, anti-cuts campaign and the account that he provided to them did not fit with their agenda."
Ms Glass said the officers must have known Mr Mitchell was under pressure to resign his post following scenes at the Conservative Party conference at which Federation members were seen wearing "PC Pleb" T-shirts.
In a statement released after the IPCC published its findings, Mr Mitchell said he and his family had "waited in vain" for Mr MacKaill, Det Sgt Hinton and Sgt Jones to be held to account.
"It is a matter of deep concern that the police forces employing these officers have concluded that their conduct has not brought the police service into disrepute," he said.
The original incident, in which Mr Mitchell was accused of calling officers guarding Downing Street "plebs" as he cycled through the main gates on September 19 last year, was the subject of a separate Metropolitan Police investigation following claims that officers conspired against the politician.
The Crown Prosecution Service is considering whether to bring criminal charges following Scotland Yard's £230,000-plus investigation, known as Operation Alice. Eight people including five police officers arrested under Operation Alice were re-bailed.
Mayor of London Boris Johnson said: "I share the frustrations of the IPCC and indeed of Andrew Mitchell and his family and indeed (Metropolitan Police Commissioner) Sir Bernard Hogan-Howe in wishing this thing were knocked on the head.
"It's got to be done, we need to get to the truth of what happened insofar as it could possibly be established for everybody's sake and it is extremely frustrating that it is taking so long.
"But the mills of justice grind slowly but they grind small, we will get the answer and that is the best we can do but we have to follow the correct procedures."
Former shadow minister for police reform and MP David Ruffley said he wanted to see a return to the Cabinet for his friend Mr Mitchell.
He told BBC Breakfast: " There is a growing view in Parliament, not just on the Conservative side, that a grave injustice has been done to Andrew Mitchell and justice demands he at least be reinstated and most of us think the Prime Minister agrees with that view and that justice will be done."
Sir Hugh Orde, president of the Association of Chief Police Officers, said the officers' behaviour had fallen below the standard expected, but their chief constables should be given the opportunity to explain their decision not to take further disciplinary action.
He told BBC Radio 4's Today: "It seems to me in this case there is no issue that the finding by the police service was the officers' behaviour fell below the standard.
"The question is the quantum of seriousness and I think that's why the chief constables are clearly determined to explain that ... to the Home Affairs Select Committee and be held to account and judged on that."
West Midlands police commissioner Bob Jones said Ms Glass's comments had been "completely unjustified" and "very inappropriate", and called for the abolition of the IPCC.
"I cannot see the point of putting cases before misconduct panels if there is not any prospect of getting any action taken whatsoever," he told BBC Radio 4's World at One. "I think that would be deceiving the public."
Mr Jones suggested the watchdog was "trying to take considerable resources away from the local police force to put it to itself", and the statements from Ms Glass and Mrs May "have not harmed that agenda".
"I do think the IPCC should be abolished and moved to a genuinely independent body that will look after the wider public interest, but obviously also ensure that police officers get a fair hearing and are treated appropriately and justly," he added.
Mr Jones said there was a stand-off between the "Westminster club" and "those who are administering policing on the ground".
But Mr Vaz told the programme that the IPCC report was "very serious".
"It just can't be ignored," he said. "You can't start wanting to abolish the organisation because you do not believe and accept the outcome.
"You have to accept the integrity. As we accept the integrity of police structures we need to accept the integrity of the police complaints process."
Mr Vaz said: "I think there is an attempt here to move the story away from the incident on to a discussion about police complaints structures. That is not really what we are about.
"We are about issues of integrity and ethics."
A Labour source said: "We think Andrew Mitchell is owed an apology. We clearly think this has gone on for too long and we need to get to the end of this investigation.
"It is right to point out that it was the Prime Minister's failure to get to the bottom of this on day one which has caused many of these problems. We called at the time for the Prime Minister to get the facts of what had happened. He failed to do that and it is a very large contributory factor in the mess we are in now."