The left-wing Guardian newspaper said the public broadcaster believed the tape was a "smoking gun" that would back up a highly controversial BBC report in May, which has provoked a furious row with Blair's office.

The story suggested that despite the reservations of the intelligence community, Blair's office "sexed up" the contents of a dossier on Iraq published last September in order to beef up the case for military action against Baghdad.

The tape recording of a conversation between arms expert David Kelly and Susan Watts, science editor of the BBC's Newsnight current affairs programme, was expected to be submitted to a judicial inquiry into Kelly's death.

The BBC said it would not discuss the contents of the tape. The state broadcaster is thought to regard it as a useful part of its evidence for the inquiry in support of its controversial story, rather than the centrepiece.

Kelly, a defence ministry consultant, was found with his wrist slashed in a wood in Oxfordshire, west of London last week, days after coming under intense scrutiny as the source for the BBC story.

After his death, the BBC confirmed that he had been the main source for their reports over concerns about the way Iraq weapons intelligence had been presented before the US-led war was launched on March 20.

On June 2 Watts quoted an unnamed source -- now revealed as Kelly -- who questioned a headline-grabbing claim in the government's Iraq dossier that Baghdad could launch weapons of mass destruction within 45 minutes.

"It was a statement that was made and it just got out of all proportion," the source said.

"They were desperate for information, they were pushing hard for information which could be released. That was one that popped up and it was seized on and it's unfortunate that it was."

The political crisis triggered by Kelly's death is Blair's biggest since he came to power in 1997, and has seen him forced to fend off calls for his resignation.

Blair -- who has been nosediving in the opinion polls, with a survey finding that 54 percent of Britons are unhappy with his performance as prime minister -- Tuesday insisted his government had "acted properly throughout" the affair.

Speaking on a flight from Shanghai to Hong Kong, as he was concluding his tour of East Asia, Blair also denied authorising the identification of Kelly.

The scientist's apparent suicide sent shock waves through political circles in Britain and has prompted the media to ask who was to blame for the way Kelly was "outed" as a suspected mole.

WAR.WIRE