Scotland Yard will abandon an investigation into the Conservative front-bencher Damian Green after a highly critical report questioned whether sending antiterrorist officers to arrest him and search his parliamentary offices was proportionate.

The review document was delivered to the Metropolitan Police yesterday by Ian Johnston, Chief Constable of British Transport Police. He spent an hour discussing his findings with Sir Paul Stephenson, the Acting Commissioner, and Bob Quick, the Met’s head of Special Operations.

The report arrived as the nine applicants for the post of Met Commissioner were cut to four. Sir Paul is believed to be on the list but Mr Quick is not.

Sir Paul called for Mr Johnston’s review of the inquiry two weeks ago in what was seen as an attempt to extricate the Met from a growing row.

David Cameron, the Tory leader, and Boris Johnson, the Mayor of London, had attacked the decision to arrest Mr Green, and Michael Martin, the Commons Speaker, came under intense criticism for letting police search an MP’s office without a warrant.

Officers from Mr Quick’s command claimed that they were right to arrest Mr Green as part of an inquiry into the leaking of information by a Home Office official, although other senior officers were appalled at the tactic.

Mr Quick said last night that he had been reassured by Mr Johnston that the arrest of Mr Green and searches of his premises were lawful. But, he added: “He [Mr Johnston] recognises that there are arguments, either way, regarding proportionality over the manner of arrest of a Member of Parliament but questions the method taken in this case. He also raises concerns as to whether elements of the investigative approach meet current policy and best practice.”

A formal decision to drop the Green inquiry is likely within days but it is not yet clear what will happen in the case of Christopher Galley, the official who leaked information to him. Sources said that Sir Paul was assessing the damage the affair had done to his chances of becoming Met Commissioner. He has been replaced as favourite for the job by Sir Hugh Orde, Chief Constable of Northern Ireland. The two other shortlisted candidates are Bernard Hogan-Howe, Chief Constable of Merseyside, and Sir Paul Scott-Lee, police chief in the West Midlands.

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