Andrew Mitchell
Andrew Mitchell was forced to resign after police officers accused him of calling them "plebs".

Andrew Mitchell, the former chief whip who was forced to resign after an altercation with police in Downing Street, has accused officers of a "dishonest" and "illicit" attempt to "blacken his name".

In a letter to the Independent Police Complaints Commission, the Conservative MP accused the police of leaking classified information to tarnish his reputation in what became known as the "'plebgate" row.

Mitchell took the action after the Sun newspaper suggested a police file passed to the Crown Prosecution Service contained no evidence that officers lied about his behaviour.

Mitchell has repeatedly denied claims, first reported in the paper, that he swore and called police officers "plebs" and "morons". He was later forced to resign as chief whip after a co-ordinated campaign by the police force, and is now suing the Sun over its claims.

A spokesman for the Sun newspaper said: "We stand by our story and will defend this claim vigorously." The Metropolitan Police said inquiries into the matter were continuing.

The police spokesman added that the Metropolitan Police had "sent a report to the Crown Prosecution Service on Thursday as part of our investigation and a copy of this file was also sent to the Independent Police Complaints Commission, as they are supervising our investigation".

Four people - including three police officers - have been arrested as part of the investigation into the incident, which happened in September last year.

A 52-year-old diplomatic protection officer was arrested last December on suspicion of misconduct in public office. Two other officers were arrested for allegedly passing information to the media and a 23-year-old man who does not work for the police was also arrested and bailed until May. All three police officers remain suspended.

According to the initial police reports, Mitchell lost his temper and swore at police when they refused to open the gates for him as he cycled out.

Mitchell admitted there was an exchange and resigned from the cabinet - but flatly denied using the word "pleb". CCTV footage of the incident cast doubt on the police reports.