Ian Johnston will report back to the Met within two weeks
A senior police officer is to investigate the handling of the inquiry into Home Office leaks which led to the arrest of Tory MP Damian Green.
British Transport Police chief constable Ian Johnston will report to the Metropolitan Police in two weeks.
MPs are angry that Mr Green, the shadow immigration minister, was held while his Commons office was searched.
Home Secretary Jacqui Smith has accused the Tories of "irresponsible and cavalier" behaviour over the leak row.
'Respect for the law'
Responding to a letter from Tory counterpart Dominic Grieve, she said suggestions that she knew Mr Green was to be arrested in advance or had been aware he was being investigated by police were "inaccurate and wholly unfounded".
You would do better to show respect for the law and duty of parliamentarians to uphold the law
She said it would have been "negligent" for the Home Office not to investigate the source of "systematic" leaks from its department - an investigation which led to Mr Green's arrest.
"Rather than seek to dismiss the offence the police are investigating, you would do better to show respect for the law and duty of parliamentarians to uphold the law," she said.
"To assert that the systematic leaking of government material is not serious if it does not relate to national security, as you and David Cameron have done, is not just a cavalier attitude to take, it is a wholly irresponsible one and entirely unfit for those who seek to hold high office."
The home secretary added she would make a statement to Parliament on the issue at the "earliest opportunity", likely to be on Thursday.
Ms Smith has said she welcomes Mr Johnston's inquiry into what she called "very serious matters".
Officers from the Metropolitan Police's anti-terrorism squad arrested Mr Green last Thursday and held him for nine hours.
They also searched all his homes and offices. The Ashford MP denies all wrongdoing and has been released on bail until February.
Dominic Grieve on the questions he wants answered
The Conservatives say Scotland Yard's behaviour was "heavy-handed", as the inquiry is into leaks of information not related to national security or covered by the Official Secrets Act.
In his letter to the home secretary, Mr Grieve said she had "utterly failed to exercise the most basic ministerial oversight over counter-terrorism police that is essential in a democratic country" in relation to Mr Green's arrest.
Mr Johnston has been asked to provide an interim report within a week and a full set of findings within a fortnight.
In a statement, the Met's acting commissioner, Sir Paul Stephenson, said he was concerned about issues raised "within the continuing debate surrounding the ongoing investigation".
He added that there would be an "urgent review of our decisions, actions and handling of the investigation to date".
Sir Paul said: "In the meantime the investigation team will be meeting with the CPS [Crown Prosecution Service] to review progress and consider next steps."
Home Secretary Jacqui Smith welcomed the decision to conduct a review of the handling of the investigation.
She said: "In view of the gravity and sensitivity of this ongoing investigation, I spoke to Sir Paul yesterday to seek his assurance that the investigation was being pursued diligently, sensitively and in a proportionate manner."
She added: "These are very serious matters, and the police should be free to pursue their investigations without fear or favour."
Mr Grieve also welcomed the review but told the BBC it was "urgent that all this is sorted out quickly".
"Until it is, parliamentarians will be unable to do their jobs properly," he added.
Liberal Democrat leader Nick Clegg said there was a danger that MPs' rights could be on a "slippery slope".
He added: "The government should be accountable to the people. That's what democracy is about.
"That can only work if opposition MPs have some power to hold the powerful to account."
Commenting on the row on Tuesday, Prime Minister Gordon Brown reiterated his earlier comment that no MP can be "above the law".
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