The row over the Iraq dossier between the BBC and the government has intensified.

The BBC's director of news released a nine-page letter to Downing Street's director of communications on Friday standing by its claims over the now infamous "dodgy dossier".

Richard Sambrook also refused to give Alastair Campbell the apology that he had demanded on Thursday.

BBC director general Greg Dyke also said the corporation would stand firm despite "unprecedented pressure" from Number 10.

The row continued as Jack Straw appeared before the Commons foreign affairs committee for the second time within a week.

The foreign secretary maintained that the decision to go to war was based on sound intelligence and denied that any evidence had been misrepresented or exaggerated.

"I hope very much that we find further corroborative evidence about Saddam's chemical and biological capabilities and his nuclear plans,'' he said.

"But whether or not we do, the decision to take military action was justified on March 18 on the basis of perfectly public information."

But Sambrook said the BBC would stand by its claim that the dossier used to justify war in Iraq had been "sexed up".

Joining the row, former Commons leader Robin Cook, claimed the issue was a minor sideshow distracting attention from the main issues.

"It's very important that we don't get distracted into the argument about deception and sexing up or whatever - these are not allegations that I have personally ever made," he told the BBC.

"For me, the real issue is that we were told things as a justification for war which have plainly turned out to be wrong since the war was over."

Tony Blair made his displeasure known by snubbing the BBC during a press conference with President Putin.

On Thursday the prime minister's official spokesman took the unusual step of publicly demanding answers to 11 questions that "are still relevant".

"We are still looking for an apology," added the spokesman.

Number 10 refused to rule out making an official complaint to the Broadcasting Complaints Commission.

And it did not rule out the possibility of taking legal action against the BBC correspondent Andrew Gilligan.

"We are not going to speculate about what may or may not happen. What is important is that we get the record straight," said Downing Street.

Number 10 demanded to know if the BBC's source was a member of the Joint Intelligence Committee, why it had not checked the story with Number 10 and if its source was more reliable than the prime minister, foreign secretary, the heads of the intelligence services and other government figures implicated in the row.

"We are simply asking whether they believe they are in effect calling all those people liars," said the spokesman.

The war of words between the government and the BBC continued after the broadcaster claimed Campbell was attempting to distract attention from reports that the case for war against Iraq were "sexed up".

The corporation's news and current affairs chief, Richard Sambrook, said Campbell's latest attack was an attempt to divert attention from its central charge.

"Alastair Campbell can try and pretend we said all sorts of things we didn't say. We are absolutely clear about what we said," he said.

Grilled by the Commons foreign affairs committee, Campbell had claimed the BBC had falsely reported that Tony Blair took the country to war on the basis of a lie.

The BBC says reporter Andrew Gilligan received information about Campbell's antics from a "credible" source within the intelligence services.

The government's chief spin doctor stands accused to repackaging poorly sourced intelligence to increase the level of threat posed by Iraqi weapons of mass destruction.

Speaking on Thursday Sambrook issued a point by point denial of Campbell's allegations.

"He said we had accused him and the prime minister of lying. That's not true, we haven't," he told the Today programme.

"He said we accused the prime minister of misleading the Commons. We have never said any such thing.

"He said we were trying to suggest the prime minister had led the country into war on a false basis. We've never suggested that.

"He said the BBC had an anti-war agenda. That's untrue, we have no agenda.

"Finally he said we've not apologised. Well, that is true because we have nothing to apologise for."