AN investigation by West Mercia Police initially concluded that Police Federation representatives had a case to answer for misconduct over claims they made about a meeting with former chief whip Andrew Mitchell, it has emerged.

A letter, obtained by Channel 4 News, to police chiefs from Deborah Glass highlighted that the inquiry findings changed between the draft report and the final version.

The deputy chairwoman of the Independent Police Complaints Commission (IPCC) yesterday publicly called for a misconduct panel to decide if three police officers gave a false account of discussions they had with the Tory MP at the height of the so-called "plebgate" furore.

In an email, sent today, Ms Glass wrote: "I note that in the first draft submitted to the IPCC in July, the senior investigating officer did in fact conclude there was a case to answer for misconduct, although their final report, submitted in August did not."

Mr Mitchell met the Police Federation representatives after he was accused of calling officers guarding Downing Street ''plebs'' in a foul-mouthed rant as he was asked to cycle through the main gates on September 19 last year.

But the officers were accused of deliberately misrepresenting what the MP said during the meeting in his Sutton Coldfield constituency office on October 12 last year when they gave interviews immediately afterwards.

The IPCC questioned the ''honesty and integrity'' of Inspector Ken MacKaill, Detective Sergeant Stuart Hinton and Sergeant Chris Jones and concluded that the Police Federation representatives should have faced a misconduct panel.

Earlier today, Prime Minister David Cameron insisted Mr Mitchell was owed an apology by police and said the conduct of the officers, who were representing the forces of West Mercia, Warwickshire and West Midlands, was "not acceptable".

Ron Ball, police and crime commissioner for Warwickshire, told Channel 4 News he did not know until today that the conclusion of the investigation had been changed.

He said: "I don't know why the conclusions changed. As with any prosecution eventually a judgment has to be taken as to whether or not a threshold has been reached in order to raise a complaint."

Mr Ball said he would be carrying out an inquiry into the changes made in the report conclusions.

"The first thing I will be doing when I get back tomorrow is to find out exactly what happened there because until today I didn't know," he added.

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, is the subject of a separate Metropolitan Police investigation following claims that officers conspired against the politician.

Mr Mitchell 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 in 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.

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."

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."