A police officer has been arrested on suspicion of misconduct in public office over the leak of information to national newspapers about Tory former chief whip Andrew Mitchell's tirade at officers on Downing Street.
A constable in the Diplomatic Protection Group was held on Saturday evening and bailed on Sunday to return next month, Scotland Yard said.
Mitchell resigned in October after weeks of controversy over what he was reported to have said to police after being told he could not ride his bike through the main gates.
On resigning, he insisted in a letter to Prime Minister David Cameron that he had not referred to an officer on the gate as either a "pleb" or a "moron" but acknowledged delivering the parting line: "I thought you guys were supposed to f****** help us."
The story first emerged in The Sun and transcripts of what was allegedly said appeared later in the Daily Telegraph.
Scotland Yard said that on Thursday the Metropolitan Police Service (MPS) received fresh information regarding the alleged unauthorised disclosure of information. As the result of this the Directorate of Professional Standards arrested a police constable in the Diplomatic Protection Group, on suspicion of misconduct in a public office, at 8.15pm on Saturday.
He was bailed on Sunday morning to return in January. He has been suspended from duty. The matter will be formally referred to the Independent Police Complaints Commission on Monday.
The Yard's statement said the arrest was linked to previous inquiries by the MPS as to how internal information was obtained by national newspapers following an incident at Downing Street in September. "These inquiries found no evidence to suggest any of the officers involved in the incident were involved in the unauthorised release of information. The officer arrested was not on duty at the time of the incident in Downing Street."
When he resigned Mitchell admitted the row over the incident made his position untenable. He said it was not fair to put his colleagues and family through such "damaging" stories any longer. He had clung desperately to his position amid a mounting clamour lasting a month for him to go.
Former minister David Mellor said it was "good news" that the police finally seemed to be taking leaks to the media seriously, adding: "What happened in the Mitchell case was a serious breach of duty with not only the full details of police reports being leaked, but the actual documents being handed over to newspapers. This was disgraceful. The question has to be asked, what took them so long?"
In September The Sun accused the Met of trying to "find and shoot the messenger" after it launched an investigation into the leak.
The paper said in an editorial: “To them [the Met] it’s more important to devote resources to uncovering how The Sun broke this story and attempting to expose the source who showed us evidence confirming what took place.
“As we have said, we neither paid nor offered any money for this exclusive. It is the result of what is known as journalism.
“The public interest could not be more clear-cut. Britain has a right to know if a high-ranking Government member brands police officers ‘morons’ and ‘plebs’."