A report out today says David Cameron brought in the the wrong person to investigate 'Plebgate'.
Andrew Mitchell has written a piece in which he has accused the police of trying to destroy his career in a smear campaign.
An investigation into the "Plebgate" scandal, involving Andrew Mitchell, has raised questions about leaked police accounts of the incident.
A 46-year-old female police officer from Scotland Yard's Diplomatic Protection Group was arrested over alleged leaks to the media linked to the Andrew Mitchell "plebgate" affair, the Metropolitan Police said.
A 46-year-old male officer arrested yesterday has been bailed to return on a date in March.
MPs say the police watchdog, the IPCC, should be investigating the "plebgate" affair, which involves former Gedling MP Andrew Mitchell.
Mr Mitchell quit his cabinet post as chief whip following a row over claims he called police officers "plebs".
MP for Leicester East, Keith Vaz, who chairs the Home Affairs Select Committee, says the case shouldn't have been referred to another police force to investigate.
David Cameron said it was "very important" the investigation into the 'plebgate' affair was "thoroughly carried out and proper answers are delivered".
The Metropolitan Police said the allegations against the officer arrested today are "extremely serious" and the investigation continues with "urgency, determination and an open mind."
The latest information from Scotland Yard reveals there are now six officers and one civilian arrested or being investigated over the Andrew Mitchell "plebgate" incident.
The man arrested over alleged leaks to the media linked to the "plebgate" affair was not one of the officers at Downing Street during the incident in September 2012, the Metropolitan Police said in a statement.
A police officer responsible for protecting Government officials has been arrested over alleged leaks to the media about the "plebgate" incident.
The 46-year-old from the Diplomatic Protection Group was held at his work place in central London on suspicion of misconduct in public office.
Greater Manchester Police has been asked by the Metropolitan Police to review its "Plebgate" investigation.
The Met said the move is standard practice in a high profile investigation.
Cabinet Secretary Sir Jeremy Heywood has insisted that he did a "competent" job during his investigation into the 'Plebgate' incident involving former Chief Whip Andrew Mitchell and police officers at Downing Street.
He said he told Mr Cameron that CCTV footage showed "inaccuracies and inconsistencies" in emails sent by someone who claimed to have seen the altercation last September.
Sir Jeremy said this meant they should not be relied upon in deciding whether Mr Mitchell should be sacked.
When challenged by members of the Public Administration Select Committee, about his suitability to carry out an inquiry into the incident, he said:
"It's a perfectly legitimate part of my role and frankly, I think I did the job competently and came to the right conclusion."
The Cabinet Secretary Sir Jeremy Heywood has said that after Andrew Mitchell resigned he came back in November and asked to see the CCTV footage of his row with a Downing Street police officer.
When Mr Mitchell viewed the footage, he then asked for a copy to take away.
Conservative MP, Charlie Elphicke, then asked Sir Jeremy why he did not share the CCTV footage with Mr Mitchell before he resigned given that he had previously concluded there were discrepancies between it and the police log.
Sir Jeremy said:
I'm pretty sure that he was told the broad conclusions of my report and he didn't at that point ask to see the CCTV footage. If he had asked to see it, we would have let him see it.