The "plebgate" row showed no signs of abating today as the Prime Minister insisted former Conservative chief whip Andrew Mitchell was owed an apology by police.
David Cameron's comments came after the police watchdog accused a police force of failing to properly deal with three officers accused of lying about a meeting held with Mr Mitchell in the wake of the row last year.
The Independent Police Complaints Commission (IPCC) questioned the ''honesty and integrity'' of Inspector Ken MacKaill, Detective Sergeant Stuart Hinton and Sergeant Chris Jones and concluded the Police Federation representatives should have faced a misconduct panel.
As Mr Mitchell garnered cross-party support from fellow MPs, members of the policing community lashed out at the IPCC for acting "inappropriately".
At Prime Minister's questions, Mr Cameron said the conduct of the officers, who were representing the forces of West Mercia, Warwickshire and West Midlands, 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 yesterday said it was "quite wrong" not to take disciplinary proceedings against the officers.
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."
He went on: "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."
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.
Mr Mitchell then met Mr MacKaill, Det Sgt Hinton and Sgt Jones 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", while i n comments made after the meeting Mr MacKaill claimed the former Tory chief whip refused to provide an account of the incident.
West Mercia Police conducted an internal investigation into claims 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 revealed "an issue of honesty and integrity, not merely naive or poor professional judgment" among the federation representatives.
She added: "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."
It is understood the chief constables of West Mercia, Warwickshire and West Midlands have all been asked to give evidence to the Home Affairs Select Committee next week, although their attendance is yet to be confirmed.
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."
A Labour Party 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."
And former shadow minister for police reform David Ruffley said he wanted to see a return to the Cabinet for his friend Mr Mitchell.
The Conservative MP said: " 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."
But 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 said.
"I think that would be deceiving the public."
He added: " 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."
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.
"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," he said.
" The question is the quantum of seriousness and I think that's why the chief constables are clearly determined to explain that."
Shadow home secretary Yvette Cooper said the ongoing stalemate between the IPCC and three police forces was completely unsustainable and showed that radical reforms were needed to police accountability and oversight.
She said: "It is vital for public trust in policing that we get the truth about what happened over the events in Downing Street and we are still waiting for the CPS decision.
"Andrew Mitchell has already had to wait too long for the conclusion of independent investigations.
"But there also needs to be an effective system to take action when things go wrong."
In a statement released after the IPCC published its findings, Mr Mitchell said he and his family had "waited in vain" for the three officers to be held to account.