The ex-police officer who claims he bugged an MP's visit to a jailed constituent says his life is "at risk" after the case was leaked to the media.
Mr Kearney was an intelligence officer at Woodhill Prison
Mark Kearney, a former police intelligence officer at Woodhill Prison in Milton Keynes, says he did not think it was right to bug MP Sadiq Khan.
But he claimed the Met Police put him under "significant pressure" to do so.
Shadow home secretary David Davis said bugging an MP made a "liar" of the PM because it broke previous conventions.
He spoke out as it emerged that officials in the Home Office and Ministry of Justice were told in December of the incident.
However, the BBC has learnt that Justice Secretary Jack Straw and Home Secretary Jacqui Smith had not been aware until the Sunday Times reports emerged this weekend.
Mr Davis told BBC Radio 4's Today programme that it was apparent that Mr Straw and Ms Smith were "not in charge of their departments".
"Why was this allowed to happen without any ministerial knowledge?" he asked.
"Why, when it was discovered in December, they didn't tell Jack Straw or Jacqui Smith?"
The conversations alleged to have been recorded took place in 2005 and 2006 at Woodhill Prison.
They were between Mr Khan and Babar Ahmad - a constituent and childhood friend - who is in prison awaiting extradition to the US.
He is accused there of running websites supporting the Taleban and Chechen terrorists, though he faces no charges in the UK.
Former Thames Valley Police sergeant Mr Kearney, who was working at the jail, faces charges - unrelated to the bugging claims - of leaking information to a local newspaper.
He told the BBC he was "shocked and disgusted" that the case had been leaked to the media.
"I believe it puts my life and safety at risk," he said. "I would also like to say I am quite prepared to cooperate with any inquiry so it can reach a proper conclusion."
In a statement prepared by his solicitors, Mr Kearney said there was "significant pressure from the Metropolitan Police requesting that we covertly record a social visit between a terrorist detainee and a member of Parliament".
"The MP concerned was Sadiq Khan... I did record the visit but have never felt it was justified in these circumstances," he said.
Mr Straw announced on Monday that Chief Surveillance Commissioner Sir Christopher Rose is to head an inquiry into the allegations.
He said Sir Christopher, a former Court of Appeal judge, would try to find out under whose authority any bugging was carried out and would present his findings within two weeks.
Mr Straw insisted that a chief police officer had to authorise eavesdropping operations, adding that "ministers play no part in these authorisations".
Police are entitled to monitor prisoners' communications but such operations must first be approved by the surveillance commissioner who considers them on a case-by-case basis.
However, a code known as the Wilson Doctrine forbids the covert recording of conversations between MPs and their constituents.
On Sunday Mr Khan - now a government whip - said he had no idea he might have been bugged and was pleased Mr Straw had announced a swift inquiry.