Former chief whip Andrew Mitchell is reportedly seeking assurances that Scotland Yard chief Bernard Hogan-Howe will not be involved in the "plebgate" investigation.

Mitchell puts pressure on Hogan-Howe over plebgate

Mr Mitchell is said to have doubts over Commissioner Bernard Hogan-Howe's impartiality amid growing tensions between top Tories and the police. The Times reported that Mitchell has 'lost confidence' in Mr Hogan-Howe.

Prime Minister David Cameron praised Mr Mitchell's "calm and rational" response to the "plebgate" affair today, hinting that the former chief whip could be set for a political return.

Mr Mitchell's position has been strengthened following this week's explosive developments in which a Channel 4 News investigation revealed key evidence questioning the eyewitness account of Mr Mitchell's alleged use of the word "pleb" and the official account in the police log of the incident.

The chair of the Commons home affairs committee, Keith Vaz, has claimed that a "robust, transparent and comprehensive investigation" was needed into the affair.

He called on Mr Hogan-Howe to provide the committee with an explanation of how information about the altercation entered the public domain and why the Downing Street police log "appears to conflict with CCTV evidence".

The Police Federation of England and Wales has now acknowledged concerns that it "stoked up" the so-called "plebgate" row.

Last night Paul McKeever told Channel 4 News he would apologise if "Andrew Mitchell has been done a calumny".

He added: "This is a hypothetical question as currently there is no suggestion that the officers' accounts are in question. Bernard Hogan-Howe, Commissioner of the Metropolitan Police, has made that quite clear."

Mr Cameron has now claimed Tories hold "a lot of sympathy" for Mr Mitchell's situation and revealed the pair had met at Number 10 on Monday. Police are currently investigating the possibility that the former chief whip was the victim of a conspiracy.

Speaking during a trip to Afghanistan, Mr Cameron was asked if Mr Mitchell could make a comeback and answered: "One step at a time. Let's get to the truth about what happened.

"But I think it has been an extraordinary development, frankly, to find a police officer apparently posing as a member of the public, pretending to have been outside Downing Street at the time and then trying to blacken the name of a Cabinet minister."

The prime minister said he took "full responsibility" for the investigation and stressed that the email sent to deputy chief whip John Randall did not sway his view that the chief whip did not need to resign.

"We knew this email was unreliable so it did not influence my judgment as to whether Andrew Mitchell should stay in government," he said.

Mr Cameron revealed that when Mr Randall confronted the individual who allegedly wrote the email he "flatly denied" being a police officer.

John Tully, chairman of the Metropolitan Police Federation, said: "The serious allegations aired in the Channel 4 News report are of concern to the MPF.

"We welcome and agree with Commissioner Bernard Hogan-Howe's comments that, despite any questions that have arisen, there is no reason to doubt the accounts of officers directly involved in the incident."

Mr Hogan-Howe is currently on holiday until early January.