Alastair Campbell's broadside against BBC reporting during the Iraq war backfired by making it less likely that the corporation would issue any apologies, Greg Dyke has said.

Giving evidence to the Hutton inquiry, the BBC director general said criticisms by Number 10's former director of communications had left him with no alternative but to "take some action".

Campbell had been angered by reports that he "sexed up" the government's intelligence dossier on Iraqi weapons of mass destruction.

He later widened his attack to a condemnation of the BBC's reporting of the Iraq war.

Setting out his role in the row that eventually culminated in the suicide of Dr David Kelly, Dyke said he regarded his jobs as maintaining operational "independence from government and other vested interests".

Dyke said he became aware of Number 10's concerns the initial broadcast by Andrew Gilligan on the Radio 4 Today programme after Campbell sent a letter to BBC director of news Richard Sambrook.

As the row between the corporation and the government developed, Dyke said Campbell launched "a pretty ferocious attack" on the BBC.

"Not just against the particular broadcast but on the BBC's journalistic integrity and in particular its coverage of the war," he added.

"An attack of this sort of scale from the government's director of strategy and communications was pretty near unprecedented, I would have thought."

Dyke defended the BBC's reporting, say it had not made claims against the government itself, but had reported what its source - Dr Kelly - had told journalists.

Dyke added: "[Campbell] was accusing us of lying, saying that parts of the BBC had run an agenda against the war.

"These were very serious charges to make against a broadcasting organisation."

Campbell continued his complaints with a public letter to Sambrook and a second private letter to Dyke.

The BBC director general said the letter he received was more conciliatory but had come too late.

"To this day I don't understand why Alastair Campbell didn't write to me or the chairman earlier on or ask to see either of us," said Dyke.

If the conciliatory letter had been received earlier the BBC may have had more room for manoeuvre, he added.

"He had launched a broadside against the whole of BBC journalism and by this time it seemed to me an external attack, and we had to take some action," Dyke said.

"I'm not sure there was an opportunity to put the genie back in the bottle. It was then a really very big public issue."

In addition to questioning the effectiveness of Campbell's role in the row Dyke also had strong words for Gilligan, his employee at the centre of the row.

Gilligan sent an email to a member of the Commons foreign affairs committee suggesting lines of questioning for Dr Kelly's appearance before the MPs.

He also suggested that Dr Kelly had been the source of a report by a fellow BBC reporter.

"I think we have to say this is not acceptable," said Dyke. "It is not an acceptable email to send to members of the committee."