'Plebgate': Met Police vows 'ruthless' search for truth
Metropolitan Police Commissioner Bernard Hogan-Howe has said his force would launch "a ruthless search for the truth" in the "plebgate" affair.
He spoke after temporarily returning from his Christmas holiday to deal with the Andrew Mitchell row.
Scotland Yard said he had concerns over the welfare of the officers involved.
The row broke out after the then Tory chief whip Mr Mitchell was accused of calling police officers "plebs" during an argument at Downing Street.
He later resigned, but has now told the Sunday Times he was the victim of what he says was a ploy to "toxify" the Tories.
Mr Hogan-Howe said: "The allegations in relation to this case are extremely serious. For the avoidance of doubt, I am determined there will be a ruthless search for the truth - no matter where the truth takes us."
Scotland Yard later confirmed that the commissioner had resumed his holiday on Sunday evening.
The former policing minister, Nick Herbert, called for action to tackle what he called the "cancer" of corruption within the police.
In the Sunday Times newspaper article, Mr Mitchell gives his version of the alleged altercation outside the main gates of Downing Street on 19 September.
He admits swearing after a police officer refused to let him exit through the main gate with his bicycle, but not directly at the officer, and insists he did not lose his temper or "rail against police".
He added: "These awful toxic phrases which were hung round my neck for weeks and weeks in a sustained attempt to toxify the Conservative Party and destroy my career were completely and totally untrue."
He also speaks of how "on several days I simply could not get out of bed" because of the stress involved and how "night-time was the worst".
The row began when an official police log of the incident was leaked to the media. It suggests Mr Mitchell used a number of expletives, telling the police, "you don't run this government", "learn your place", and calling the officers "plebs".
According to the note, members of the public looking on were "visibly shocked".
A serving Met police constable was arrested on suspicion of misconduct in a public office on 15 December, and has been suspended from the force over allegedly giving a false account of the incident.
Channel 4 News claimed the off-duty officer sent an email, purporting to be from a member of the public who witnessed the row, to deputy chief whip John Randall who then subsequently passed it to Number 10.
CCTV footage of the incident suggests no-one other than the officers involved were within earshot of the altercation.
Mr Mitchell said the content of the email was "completely untrue" and had left him "devastated" and the victim of a "stitch-up".
The Conservative MP Nick Herbert, who was in charge of policing until September, said a "selfish minority" of police officers had been "agitating" and had "let other police officers down".
"I think that there is an issue of corruption that is revealed potentially by this case and has taken place in other circumstances," he said.
In a statement, Mr Hogan-Howe said the force's determination to get to the truth was proved by his decision to devote 30 officers to the task and the arrest of a member of the diplomatic protection squad and a civilian.
"I believe these actions are vital in maintaining public confidence in the police," he said.
The commissioner also called for the investigation to be allowed "time and space".
The Police Federation - which represents rank-and-file officers - has launched a review into its handling of the row, following controversy over officers in the West Midlands who allegedly campaigned against Mr Mitchell.
It will appoint an independent figure to carry out the inquiry in the new year.
The prime minister, meanwhile, has rejected criticism said to come from allies of Mr Mitchell, who has claimed in newspapers that Mr Cameron left his Tory colleague "swinging in the wind".
A spokesman for the PM said he had "deep sympathy" for the former chief whip after claims emerged suggesting the possibility of "fabricated evidence against him".