Jack Straw has said an inquiry into allegations that a conversation between Labour MP Sadiq Khan and a prison inmate was bugged may be completed in two weeks.
Outlining the different systems of approval needed to carry out surveillance, the justice secretary said that the case in question was an operation "sought by and authorised by the police".
Such instances, he said, came under the supervision of the chief surveillance commissioner, Sir Christopher Rose.
The former senior court of appeal judge had agreed to conduct a "fact-finding" inquiry, Straw told MPs, which he hoped to conclude within two weeks.
The Commons statement came the day after the Sunday Times reported it had seen a document showing that despite internal police concern, the bugging operation had gone ahead.
Khan, a government whip, was said to have been recorded while speaking to a constituent and friend, Babar Ahmad, who is being held in prison.
Ahmad is awaiting deportation to the USA over the alleged running of a website raising funds for Taliban and Chechen terrorists in the 1990s.
The paper said the eavesdropping had taken place at Woodhill Prison in 2005 and 2006 using a microphone hidden in a table.
Bugging an MP breaches the 'Wilson doctrine', which has expressly forbidden eavesdropping on parliamentarians since 1966.
Shadow home secretary David Davis said the justice secretary had "told us what should have happened, not what did happen".
"By now, he should be able to answer the question 'who authorised this?' Was it a minister, was it a policeman?" he asked
5 February 2008