Justice Secretary Jack Straw was aware last December that Labour MP Sadiq Khan had met with a terrorism suspect in prison, but had not heard suggestions their conversations were bugged, the government said on Tuesday.

The secretary had told the House of Commons on Monday that he was first alerted on Saturday February 2 to reports that the conversations had been bugged after the Sunday Times approached his office.

The allegations of bugging suggest that the so-called Wilson Doctrine, under which security services and police do not record conversations of members of parliament, may have been violated.

The Justice Ministry press office said prison officials were aware in December that the press was interested in Khan's visit to Woodhill Prison in Milton Keynes - including suggestions he may have been bugged.

But it said Straw was not aware at the time that any element of this story included a bugging allegation.

"No submission was received by the Ministry of Justice private office on this issue," the ministry said in a statement.

"The Justice Secretary's impression at this time was that this was an attempt at a smear story about Sadiq Khan MP and his involvement with a prisoner," it said.

Straw announced to the House on Monday an immediate inquiry into the report that Khan, MP for Tooting and a former human rights lawyer, had been bugged.

The Sunday Times said anti-terrorist police had bugged Khan's conversations with Babar Ahmad, a prisoner fighting extradition to the United States where he is accused of running Web sites supporting terrorism.

Meanwhile, a former policeman accused of carrying out the bugging said he thought the operation was unjustified but felt under pressure to carry it out, newspapers reported his lawyers as saying.

Former Detective Sergeant Mark Kearney, who worked for Thames Valley Police, said the pressure to secretly tape the conversations came from colleagues in the London force.

In a court statement from his lawyers reported by the BBC, 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," the statement added.

Police have been forbidden to eavesdrop on Westminster politicians since a bugging scandal involving Labour Prime Minister Harold Wilson's government 40 years ago.

A Metropolitan Police spokeswoman declined to comment.