No 10 insists Kelly tape backs its case against the BBC

The Government will tell the inquiry into the death of David Kelly that a tape recording of him - which was purported to be the BBC's "smoking gun" - actually supports Downing Street's case against the BBC reporter Andrew Gilligan.

In the recording, Dr Kelly says that the intelligence services included the claim that Saddam Hussein could deploy chemical and biological weapons within 45 minutes in a government dossier on Iraqi weapons. Downing Street argues that information contradicts Mr Gilligan's allegation that the statement was inserted against the wishes of the intelligence services. "We think the tape helps us and not the BBC," a government source said yesterday.

In a recorded conversation with Susan Watts, the science editor of BBC2's Newsnight, Dr Kelly says the Government's "45 minutes" claim "got out of all proportion".

The Guardian reported yesterday that the BBC believes the tape is the "smoking gun" to exonerate Mr Gilligan, who claimed on Radio 4's Today programme the "45-minute claim" was inserted in last September's dossier "at the behest of Downing Street". He later named Alastair Campbell, Tony Blair's director of communications, as responsible.

After Dr Kelly's apparent suicide, the BBC admitted he was the main source for Mr Gilligan and Ms Watts in their reports about the Government's claims over Iraq's arsenal. On Newsnight on 2 June, Ms Watts used an actor's voice to speak Dr Kelly's words. On the 45-minute warning, her source said: "It was a statement that was made and it got out of all proportion. 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."

In its battle with the Downing Street machine, the BBC has repeatedly drawn attention to Ms Watts' coverage. At first glance, the Newsnight report appears to back up Mr Gilligan's allegation.

But No 10 officials are convinced that Ms Watts' reports will support their case that Mr Gilligan's original claim was wrong. In its evidence to the judicial inquiry to be headed by Lord Hutton, the Government will cite another report by Ms Watts on 4 June. She said then: "Our source was not disputing that the 45-minute assessment was included in the dossier by the intelligence services, although he did say he felt that to have been a mistake."

The Government will also tell Lord Hutton that Ms Watts did not repeat Mr Gilligan's claim that Mr Campbell "sexed up" the dossier

The BBC will argue that Dr Kelly gave Mr Gilligan different information to Ms Watts and Gavin Hewitt, who reported the story for the 10 O'Clock News on BBC1. A BBC source said: "I believe we can prove that Dr Kelly did say to Mr Gilligan things that he did not say to Susan Watts or Gavin Hewitt. The contemporaneous notes are good and we believe that we have found some quite strong circumstantial, corroborative evidence."

The BBC team preparing for the inquiry is headed by Mark Damazer, the deputy director of news.

While standing by Mr Gilligan's report, the BBC will admit that mistakes were made by BBC presenters when they discussed it.