David Mitchell
Andrew Mitchell: Exonerated over Plebgate (Reuters)

The so-called Plebgate scandal which saw senior government minister Andrew Mitchell forced to resign after a clash with security officers at the gates of Downing Street has dramatically deepened with the launch of a fresh inquiry amid claims of a police whitewash at the highest level.

The Chief Constable of West Mercia Police, David Shaw, revealed that he had asked HM Inspector of Constabulary to re-evaluate all the evidence surrounding the incident, which could yet lead to misconduct proceedings against officers at the heart of the affair.

And he revealed he had written a personal letter to Mitchell offering him a "profound and unreserved apology" for the effect it had had on him.

His announcement came after three officers involved in the affair were accused of lying as part of a conspiracy to discredit and bring down a member of the government as part of their campaign against cuts to the police service.

And it followed evidence from those officers in which they denied any conspiracy, insisted they had done nothing wrong other than errors of judgment in talking to the media, and said they still believed it had been right for Mitchell to have resigned over the affair.

Committee chairman Keith Vaz however told them that their evidence had been "most unsatisfactory".

What most concerned the Home Affairs Committee was that an original inquiry into the affair had led to a recommendation that the three officers should face misconduct hearings. That was overruled by other officers who found they had no case to answer.

But the MPs heard Deborah Glass, the deputy chair of the Independent Police Complaints Commission, which had oversight of the inquiry, say she believed the charge should have been the more serious one of gross misconduct which could have led to dismissals.

The highly unusual evidence session led to Tory MP Michael Ellis suggesting there had been a whitewash at the highest level and allegations that the entire incident had been part of the Police Federation's campaign against government cuts.

The complex and sometimes baffling series of events which has seen officers arrested pending inquiries started when Tory chief whip Mitchell was stopped from riding his bicycle through the main gates at Downing Street.

He admitted to swearing at police but denied officers' claims that he had called them "plebs", the issue that ultimately led to his resignation.

That incident is the matter of a separate investigation but it is the subsequent "clear the air" meeting between three other officers and Mitchell to get to the bottom of the original incident that has sparked the latest drama.

While the original incident still remains to be resolved, the subsequent series of inquiries have been exposed as deeply flawed and both prime minister David Cameron and home secretary Theresa May have demanded a police apology.