The chief of the Secret Intelligence Service, MI6, yesterday publicly defended the claim in the Government's Iraq dossier that some chemical and biological weapons could have been deployed in 45 minutes.

In an unprecedented session of the Hutton Inquiry, Sir Richard Dearlove said the intelligence had been "well sourced" and its inclusion in the dossier had been valid.

However he admitted, "with hindsight" that the way it had been presented had been open to "misinterpretation" by the public.

On the opening day of the second phase of the inquiry, the director general of the BBC, Greg Dyke, also admitted the corporation had lessons to learn from the events leading up to the death of the Government weapons expert David Kelly.

He said it was "not acceptable" that the Today programme journalist Andrew Gilligan had disclosed to MPs that Dr Kelly was the confidential source of the story by another BBC journalist about the Iraq dossier.

However, the day was dominated by the evidence of Sir Richard, who became the first MI6 chief to give evidence in any kind of public forum.

The spymaster - who has never had a contemporary photograph of himself published - did not appear in person, but gave evidence through an audiolink. He immediately took issue with the suggestion that the 45-minute point in the dossier had just been a "claim".

"You use the word 'claim'," he told counsel to the inquiry James Dingemans QC. "I would prefer to refer to it as a piece of well-sourced intelligence."

He acknowledged the information came from a single source but rejected the suggestion that meant it was unreliable.

Sir Richard did, however, accept criticism in the reports by the Parliamentary Intelligence and Security Committee (ISC) and the Commons Foreign Affairs Committee (FAC) about the way the 45 minute intelligence was presented in the dossier.

The ISC said that it was "unhelpful" that the dossier failed to make clear that the intelligence referred to battlefield weapons rather than ballistic missiles while the FAC said it was given undue prominence.

In his evidence, Mr Dyke said the BBC had faced a "ferocious" Government attack over Mr Gilligan's report on Radio 4. "One felt that a lot of scores were being settled, particularly in terms of the coverage of the war," he said.

However, he acknowledged that with hindsight he would have handled the complaint differently. "I've no doubt that there will be lessons for all of us to learn but there will certainly be lessons for the BBC," he said.