Mark Kearney faces eight charges of misconduct in a public office in allegedly leaking police information to a local newspaper journalist and a private detective.

He was charged after an investigation by Thames Valley Police — the force in which he served for 30 years — and is expected to enter pleas at Kingston upon Thames Crown Court before a trial this year.

In a series of defence statements, Mr Kearney says that he was part of a secret intelligence unit at Woodhill prison, near Milton Keynes, which bugged visits and telephones.

Mr Kearney says that he recorded the conversations of Sadiq Khan, MP, when he visited Babar Ahmad, a terror suspect, in 2005 and 2006. He says the bugging was carried out at the request of the Metropolitan Police, which had been monitoring Mr Ahmad’s communications since he was arrested on an American extradition warrant in 2004.

The former officer has also stated that he was asked by West Midlands Police to listen in when another terrorist inmate was visited by his solicitor.

Mr Kearney also says that he was asked by a former Thames Valley chief constable to leak stories to the press to influence the findings of a royal commission that was examining the criminal justice system.

He alleged that in the early 1990s Sir Charles Pollard asked him to plant stories about criminals who escaped justice by exercising their right to silence. Sir Charles had made submissions on the subject to the Royal Commission on Criminal Justice, chaired by Lord Runciman.

Chris Huhne, the Liberal Democrat home affairs spokesman, has called on Jack Straw, the Justice Secretary, to widen the scope of the investigation into the bugging of Mr Khan to include allegations of breaches of legal privilege.

“It seems to me crucial that we now know how extensive the police bugging operations of lawyer-client discussions at British jails have been,” Mr Huhne said in a letter to Mr Straw.

“Either ministers knew what was going on and were complicit in a wholesale undermining of the principle of lawyer-client confidentiality, or they have been so unaware of what is going on in their own departments as to connive unwittingly in a policy disaster. Extensive bugging may now lead to the quashing of unsafe convictions, and also to ineffectiveness in bugging for serious terrorist incidents, which are likely to be an imminent threat to public security. This is a wholly counter-productive policy.”

Geoffrey Robertson, QC, said there needed to be an immediate investigation into suggestions of widespread bugging at the prison of inmates and lawyers. He said that if eavesdropping had occurred during legal visits, there could be a series of successful appeals.

Three other defendants are to stand trial with Mr Kearney. Sally Murrer, a journalist, faces three charges of aiding and abetting misconduct in a public office; Derek Webb, a private detective, faces five aiding and abetting charges; and Mr Kearney’s son, Harry, faces one similar charge.

The Times understands that a senior Thames Valley police officer will be questioned about the “surveillance society” by the Home Affairs Select Committee next month. Assistant Chief Constable Nick Gargan, a national police spokesman on covert investigation, is certain to face questions about the Kearney affair and bugging inside Woodhill jail.

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