A police officer under investigation over claims he witnessed a row in Downing Street involving a Cabinet minister "wasn't there at the time", the Metropolitan Police Commissioner has said.
The arrest of a diplomatic protection squad member did not appear to affect the account of officers on the scene of the so-called plebgate spat with Andrew Mitchell, Bernard Hogan-Howe insisted.
The Independent Police Complaints Commission said it is supervising an investigation into the "validity" of the officer's claim, believed to have been made to an MP.
Scotland Yard made the arrest, on suspicion of misconduct in public office, and suspended the individual from duty after fresh information emerged from a leak inquiry.
It remains unclear to what extent, if any, the case is linked to the appearance in national newspapers of details from the official police log of the incident.
Mr Hogan-Howe said "there is more to this than meets the eye" and that he believes the arrest will prove justified when all the facts can be revealed.
Mr Mitchell resigned as chief whip in October after weeks of controversy over an angry exchange when he was told by police in Downing Street that he could not ride his bicycle through the gates.
He admits swearing at an officer but denies calling him a "pleb" or a "moron", insisting parts of a police log of the incident published in the media were "false".
The arrest raised speculation that the ex-minister could be vindicated.
But Mr Hogan-Howe told London's LBC 97.3 radio: "I don't think, in terms of what I've heard up to now, that it's really affected the original account of the officers at the scene. Because of course this officer we've arrested wasn't any of those people involved originally. This is another officer who wasn't there at the time."
In a separate BBC interview, he said: "There is more to this than meets the eye. I am afraid I am constrained in explaining that and I hope that when people hear the full story they will support what we've done.
"We got some new information, we acted on it quickly and I hope, in time, when we are able to explain the sequence of events, people understand why we did what we did."
It is understood that London Mayor Boris Johnson has discussed with the commissioner his concerns over the latest developments in the case.
The story of the set-to emerged in The Sun newspaper and transcripts of what was allegedly said, including those insults, appeared later in The Daily Telegraph.
Mr Mitchell accepts that one of his parting shots to the on-duty officer was: "I thought you guys were supposed to f****** help us."
But he continues to contest other elements of what he is alleged to have said.
He told ITV News: "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."
Scotland Yard has said there is "no evidence to suggest any of the officers involved in the incident were involved in the unauthorised release of information".
The arrest has been criticised by Met Police Federation chairman John Tully who said it appeared disproportionate and could be the subject of legal challenge.
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