Ministers faced anger over the advance of Britain's "surveillance society" as an official report confirmed that police had bugged a the private conversations of a Labour MP.
The report, conducted by Sir Christopher Rose, the chief surveillance officer, confirmed that five junior officers who monitored two meetings between Sadiq Khan and one of his constituents had done so knowing he was an MP.
But they had received proper authorisation to listen in and did not breach the legislation controlling surveillance operations, the report concluded. Mr Khan was recorded by a bug hidden in a desk when he visited the terrorist suspect Babar Ahmad in Woodhill jail, Milton Keynes, in May 2005 and June 2006.
MPs expressed concern that the "Wilson doctrine", which forbids the tapping of MPs' telephones, had been flouted.
Dominic Grieve, the shadow Attorney General, said: "This also raises wider issues about the extent to which we now have a level of surveillance society where a very large number of areas of intrusive investigation are being authorised by police officers at a senior level but carried out and monitored by police officers at a very junior level."