Why was whistleblower in bugging of Muslim MP scandal not quizzed during inquiry?

Mark Kearney claimed he was put under pressure to record prison meetings between Mr Khan and a friend who is fighting extradition to the U.S. on terrorism charges.

He has said he fears for his safety after revealing the Special Branch operation.

MPs expressed surprise that the inquiry ordered by Jacqui Smith last month did not call Mr Kearney to give evidence.

And they complained that it ignored damaging allegations that the police now routinely bug conversations between lawyers and their clients.

Shadow Attorney General Dominic Grieve said he had "considerable cause for concern" about aspects of the report by Sir Christopher Rose, the interception commissioner.

He singled out the decision not to question Mr Kearney, the former detective who carried out the bugging operation in Woodhill prison, Milton Keynes.

Mr Kearney, who is facing trial on charges of leaking police information, claims he was put under pressure to bug Mr Khan.

His MP, Tory Andrew Selous, said Mr Kearney was "very surprised" he had not been asked to co-operate.

He added: "Both he and the journalist with whom he is charged are concerned that because of the range of activities they are aware of at Woodhill Prison, there may be an attempt to silence them."

Sir Christopher found that five police officers knew Mr Khan was an MP, but were not aware of rules that bar the bugging of parliamentarians.

He said there was confusion over the Wilson Doctrine, which for more than 40 years was supposed to protect MPs from intrusive police surveillance.

Reporting the inquiry findings to the Commons yesterday, Miss Smith said she will amend statutory codes of practice to offer MPs the same legal protection as priests and lawyers when they are speaking to constituents.

But that could bring objections from civil liberty groups who will ask why MPs should be given protection not available to the public.

The inquiry was ordered after it emerged that conversations between Mr Khan and his childhood friend Babar Ahmad were targeted by Special Branch on two occasions in 2005 and 2006.

The revelation caused uproar at Westminster when it was revealed that the bugging had been sanctioned by senior officers.

Miss Smith yesterday denied that Mr Khan had been deliberately targeted. She confirmed that two detective constables and three junior officers knew he was an MP, but "had no reason to regard this as significant".

The report found that senior officers, including former Scotland Yard terror chief Andy Hayman, did not know Mr Khan was an MP.

The Wilson Doctrine was introduced by the then Labour Prime Minister Harold Wilson in 1966 at the height of the Cold War, amid claims that MPs were being targeted by the security services.

Liberal Democrat spokesman Tom Brake said it was "astonishing" that Sir Christopher had concluded, after just a fortnight of investigation, that widespread bugging was unlikely to be happening.

He added: "I hope you will consider, as the Law Society has suggested, that it may be appropriate to have an inquiry into whether a much larger- scale bugging is indeed taking place."