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.
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.
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.
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.
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.
Novelist Robert Harris, a friend of Mitchell's for 35 years, said revelations about the row, due to be aired tonight on Channel 4 News, would help to "transform" the story.
He told BBC Radio 4's World At One programme: "I think there is, I gather, evidence that casts serious doubt on the way in which the whole matter was handled."
He added: "I think it will completely transform the story, I don't think there is any doubt about that.
"I think people will, for the first time, begin to see that there are two sides to this whole event. Whether that will lead to his recall to the front rank of government, I don't know.
"I think the most important thing for him at this stage is to clear his name, to get his honour back, because at the moment he is a pretty trashed figure."
Harris said it "didn't ring true" to him that Mitchell would use words like pleb or moron.
Asked about suggestions that the Mayor of London was extremely concerned about the arrest of a police officer linked to the row, he said: "As I understand it, Boris Johnson was objecting to the idea of a whistleblower being picked up by the state and silenced and that is something all of us would think is horrible, but if, on the other hand, it does turn out to be a police officer sending an email that is false to an MP just before The Sun goes to press then I don't think that is the sort of activity that the Mayor of London should be defending."