Pc Keith Wallis, who lied about witnessing the Plebgate row, was jailed for 12 months at the Old Bailey today for misconduct in a public office.
He admitted a charge of misconduct in public office for sending a letter to his own MP John Randall, who was Mitchell's deputy chief whip, claiming to have witnessed the row at the gates of Downing Street.
The scandal began when then chief whip Andrew Mitchell MP became involved in a heated confrontation with another police officer, Toby Rowland, after he was refused permission to cycle through the main gate.
The Sutton Coldfield MP, who was forced to quit as chief whip over the debacle, later admitted swearing but denied Pc Rowland's claim that he used the word ''pleb''.
Last month, the Old Bailey heard how Wallis, who is from the Metropolitan Police diplomatic protection group, admitted his offence in a police interview and offered to resign.
Following Wallis's guilty plea last month, Mitchell said justice had been done and there were calls for his return to Government.
Met commissioner Sir Bernard Hogan-Howe apologised to Mitchell and said that Wallis's behaviour fell "way below the standards expected" of his officers.
Cameron also issued a statement saying it was "completely unacceptable" for police to falsify their account of an incident.
Mr Justice Sweeney said: "Passing sentence on you I am in no position to decide precisely what happened between the officers and Mr Mitchell in Downing Street nor do I need to do so, but it is absolutely clear what did not happen - you were not an independent member of the public, you were not present, neither was your nephew, and neither of you witnessed the incident.
"Yet, over a total period of nearly three months you pretended to your Member of Parliament and initially to the interviewing officers that all of those things were true including involving your nephew in the process."
Sweeney went on: "This was thus sustained, and in significant measure, devious misconduct which fell far below the standards expected of a police officer. Indeed it was a betrayal of those standards, and was misconduct which as well as having had an impact Mr Mitchell himself, has had a significant impact on public trust and confidence in the integrity of police officers."
He added that police officers "must be deterred from misconduct and the public must be able to see that punishment will be visited upon police officers who betray the trust reposed in them".
Earlier, the court heard that "rumour and gossip" incensed Wallis, and combined with high emotions over the killing of two female officers in Manchester the day before.
It was in this state that Wallis got drunk after his shift and went home to send the late night email full of spelling mistakes and capital letters to Randall.
Despite stating he did not believe Mitchell should lose his job, events "got completely out of hand", his lawyer Patrick Gibbs QC said.
Randall's interest in the case in Westminster, combined with media involvement, escalated the situation and Wallis did not have the mental capacity to come clean and put a stop to it, the court heard.
He was caught out in the lie when CCTV showed he was not at the Downing Street gates with his nephew at the time of the row with Mitchell, as he had claimed.
But Gibbs insisted there was no conspiracy at play, rather Wallis had convinced himself he had witnessed the incident on September 19 2012.
Gibbs said: "While it is impossible to pinpoint the moment Mr Wallis came to believe that video in his head, he did genuinely come to believe it."
Mr Gibbs said Wallis, who served for 30 years, suffered from both mental and physical illness and had been deeply affected by the death of his father, who was also a police officer.
Appealing to the judge not to send him to jail, Gibbs said: "He would be the ideal scapegoat for more sophisticated men but sending him to prison would be to mistake this for what it is not."
Wallis's emails to Randall were read out by prosecutor Zoe Martin.
In the email of September 20, he says: "I write to complain at the absolutely digesting (sic) behaviour displayed by your fellow member of parliament."
He goes on to describe going to Downing Street with his nephew who was visiting from Hong Kong in the hope of seeing the Prime Minister.
The nephew spotted Mitchell and mistook him for London mayor Boris Johnson engaged in what Wallis described as "yobbish and loutish" behaviour.
Describing himself as a driver, Wallis wrote that tourists were "shocked" at the row and some were filming it.
He said Mitchell was swearing and made the now disputed claim that he called an officer a "pleb" as he was barred from cycling through the main Downing Street gate.
Complaining at Mitchell's "unacceptable behaviour", he says: "If you are in a position of authority you can say whatever you like to the police because you are more important than anybody else."
Wallis wrote that he "did not expect anything to come of it" but Randall did take up the complaint and tried repeatedly to get hold of his constituent.
An investigation got under way at Westminster and a story ran in The Sun the following day.
As the situation intensified, a Channel 4 news team went to his home and confronted him about the email. Wallis claimed not to know about it.
By December, Wallis seemed upset at work and his sergeant suggested he take time off, the court heard.
Wallis told a member of the Police Federation about contacting his MP because he was "disgusted by the incident", saying he had not mentioned he was a police officer.
Police who were investigating the incident eventually found out Wallis was a constable and he was arrested for misconduct in a public office.
Wallis told officers: "I knew I should have thrown myself under a train yesterday."
Initially Wallis stuck to his story but when confronted by the CCTV evidence, he came clean, the court heard.
He told police: "I eventually convinced myself I was there...I totally believed I was there.
"I thought in a stupid, naive pathetic way I was backing up my colleagues. I just convinced myself I was there."
He went on to apologise for letting down the Metropolitan Police, his family and Mitchell.
Zoe Martin said that Wallis was "mortified by the disgrace" of his actions.