13.35 UPDATE: 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, of West Mercia Police, 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 today, 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 full story is below
THE "honesty and integrity" of police officers - including West Mercia Inspector Ken MacKaill - has been called into question by a police watchdog after an investigation into last year's 'plebgate' affair.
The Independent Police Complaints Commission (IPCC) said Inspector Ken MacKaill, chairman of the West Mercia Police Police Federation, Detective Sergeant Stuart Hinton of Warwickshire Police and Sergeant Chris Jones from the West Midlands force, should have faced misconduct hearings over comments about what chief whip Andrew Mitchell said in a private meeting about the incident.
Mr Mitchell was accused of calling officers in Downing Street 'plebs' after he was not allowed to use a gate to leave on his bicycle on September 19 last year.
The Police Federation trio met with the minister on October 12, shortly after the affair, in a bid to clear the air.
But immediately after the meeting, they addressed the media, claiming the former chief Tory whip refused to give an account of the incident.
However, a transcript shows Mr Mitchell apologised for swearing at the police officers but denied using the word "plebs" during the meeting.
He resigned on October 19 as the fallout continued.
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.
But the IPCC investigation claims they should have faced action.
IPCC deputy chairwoman Deborah Glass said the evidence revealed "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."
Now, the West Mercia force's chief constable, David Shaw, has been summoned to give evidence to the Home Affairs Select Committee on the issue.
In a joint statement with the Warwickshire and West Midlands forces, West Mercia Police defended its handling of the investigation.
It read: "Andrew Mitchell MP has never made a complaint to police. West Mercia, with the support of West Midlands and Warwickshire Police, recognising the public interest in this case, independently decided to investigate this incident and made a referral to the Independent Police Complaints Commission.
"We asked for the matter to be independently investigated by the IPCC because we recognise the significant public interest in the matter, however this was declined.
"The IPCC have supervised this investigation throughout and have been invited to reconsider their position on more than one occasion.
"The decisions following this investigation were carefully considered, with the support of appropriate legal advice.
"Warwickshire, West Mercia and West Midlands Police have separately considered the findings of the investigation and all three forces agree on the outcome."
West Mercia police commissioner Bill Longmore expressed surprise about comments by IPCC deputy chairwoman Deborah Glass and said he was seeking an urgent meeting with Home Secretary Theresa May.
"Given the critical statement which the IPCC Deputy Chair has made in the last few hours, I am frankly surprised the IPCC did not resume conduct of the investigation - they certainly had the power to do so," he said.
Andrew Mitchell resigned over the affair
In a statement released after the IPCC published its findings, Mr Mitchell said he and his family had "waited in vain" for Mr MacKaill, Mr Hinton and Mr 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.
"Most people will disagree. It is a decision which will undermine confidence in the ability of the police to investigate misconduct when the reputation of the police service as a whole is at stake.
"My family and I have waited nearly a year for these police officers to be held to account and for an apology from the Police Forces involved. It seems we have waited in vain."
The chairman of the Police Federation, Steven Williams, questioned the intervention by the IPCC.
"My concern is that by releasing her [Ms Glass'] personal view that she disagrees with the findings of the West Mercia investigation she displays a lack of independence," he wrote in a letter to Mrs May.
"This threatens to undermine the considered findings of the investigation in the eyes of the public, whereas in fact those investigating and deciding the case are the proper arbiters in this matter."
Eight people have been arrested over the original incident, in which Mr Mitchell was accused of calling officers guarding Downing Street "plebs" as he cycled through the main gates.
The incident was the subject of a separate Metropolitan Police investigation following claims officers conspired against the politician.
Giving evidence to MPs, Mrs May said: "The IPCC statement makes troubling reading. If it is indeed the case that warranted police officers behaved in the way Deborah Glass has described, that's not acceptable at all."
Asked if the chief constable of West Mercia Police should apologise to Mr Mitchell, Mrs May said: "I think that would be appropriate."
She added: "The police need the trust of the public. These sorts of incident will strike at the heart of that issue of trust."