A Met Police officer accused of falsely claiming to have witnessed the Andrew Mitchell "plebgate" incident has pleaded guilty to misconduct in a public office.

PC Keith Wallis, 53, claimed to have witnessed an argument between the former chief whip and officers at the gates 10 Downing Street in September 2012.

Mitchell resigned from his role as chief whip despite frequently denying accusations that he had called a police officer guarding the gates of 10 Downing Street a "f*****g pleb".

Mitchell admitted swearing during the incident in September 2012 but denied swearing at the officers when they asked him to use the pedestrian gate rather than allowing him to take his bicycle through the main gates.

Wallis claimed to have witnessed the event in an email to his MP John Randall, who is the Conservative deputy chief whip. After pleading guilty to misconduct charges at the Old Bailey, Wallis offered his resignation from the force. He is due to be sentenced in February.

Wallis will also face a misconduct hearing at the conclusion of all legal proceedings in relation to "discreditable conduct, honesty and integrity, and/or improper disclosure of information", Met police have said.

Following Wallis' guilty plea, Mitchel said he is "pleased justice has been done".

He added: "It is very sad and worrying for all of us that a serving police officer should have behaved in this way. There remain many questions unanswered, in particular why PC Wallis wrote this email and who else was involved in this process."

Metropolitan Police commissioner Sir Bernard Hogan-Howe said he will be apologising to Mitchell personally and Wallis' actions have "negatively impacted" public trust in police officers.

He added: "This investigation has been a ruthless search for the truth as at the heart of this are extremely damaging allegations that officers have lied and falsified statements against a Cabinet Minister.

"The evidence against PC Wallis was such that he has entered a guilty plea. To lie about witnessing something and provide a false account falls way below the standards that I and PC Wallis's colleague expect of police officers. His actions have also negatively impacted upon public trust and confidence in the integrity of police officers.

"I would also like to apologise to Mr Mitchell that an MPS officer clearly lied about seeing him behaving in a certain manner. I will be writing to him offering to meet and apologise in person.

"I expect my officers to serve the public without fear or favour, where officers break the law they must expect to be held to account and answer for what they have done."

Wallis and four other officers, all from the Metropolitan Police Diplomatic Protection Group, are facing gross misconduct disciplinary proceedings. The four other officers could lose their jobs.