A Metropolitan Police officer has been arrested over the leak of information about ex-Chief Whip Andrew Mitchell's tirade against police on Downing Street.
The unnamed constable with the Diplomatic Protection Group was arrested on Saturday on suspicion of misconduct in public office before being bailed on Sunday.
"The officer has been suspended from duty," a Met Police statement said.
"The arrest is linked to previous inquiries by the MPS (Met Police Service) as to how internal information was obtained by national newspapers following an incident at Downing Street in September.
"The officer arrested was not on duty at the time of the incident in Downing Street."
Mr Mitchell resigned as Conservative Chief Whip in October after weeks of controversy over an angry exchange with police who told him he could not ride his bike through the gates at the end of Downing Street.
In a letter to Prime Minister David Cameron he insisted he had not referred to an officer on the gate as either a "pleb" or a "moron".
However, he did acknowledge saying: "I thought you guys were supposed to f****** help us."
Mr Mitchell stressed again on Monday that he did not accept the version of events recorded in the police log.
"I'd just like to reiterate once again, that it's the contents of the alleged police log which are false... They are false and I want to make that very clear," he told ITV News.
The Prime Minister's spokesman said the issue was being handled by the police and refused to comment on the whistle blower's arrest.
Deputy Prime Minister Nick Clegg, when asked if the arrest was a proportionate response, said it would be "wrong" for politicians to jump in.
"It's not for politicians to do at all," he said during questions following a speech in London.
"Obviously this is a controversial issue but I really think it should be left for the police and the prosecuting authorities to make up their own minds."