The prime minister has angrily denied reports that the government invented intelligence about Saddam Hussein's arms programme.

Speaking in Warsaw, Tony Blair insisted he had "absolutely no doubt" that British intelligence about Iraq's weapons of mass destruction was credible and accurate.

Following reports challenging the government's claims about Saddam Hussein's weapons arsenal the premier took his critics head on.

In an emphatic performance, Blair said the suggestion that intelligence was hyped to make the case for war was "completely absurd".

"The evidence that we had of weapons of mass destruction was evidence drawn up and accepted by the joint intelligence committee," he said.

"That evidence of weapons of mass destruction is evidence the truth of which I have absolutely no doubt about at all.

"The idea that we authorised or made our intelligence agencies invent some piece of evidence is completely absurd."

And he warned that critics were merely attempting to settle old scores.

"What's happening here is that people who have opposed this action throughout are now trying to find a fresh reason for saying it wasn't the right thing to do," he said.

"When you go to Iraq and talk to people there and see the freedom they have, you realise why it was emphatically the right thing to do.

"When you say there is no evidence that weapons of mass destruction existed in Iraq, there are 12 years of United Nations resolutions about the weapons of mass destruction found in Iraq.

"There's no doubt about the chemical programme, the biological programme, indeed the nuclear weapons programme."

Blair's intervention came amid widespread reports that Downing Street doctored intelligence to shore-up support for the Iraq conflict.

A senior intelligence official told the BBC that Number 10 wanted the government dossier on Saddam's weapons capability "sexed up".

Friday's Independent quotes a senior minister saying that a failure to locate weapons of mass destruction would represent "Britain's biggest ever intelligence failure".

"We would have to look at the whole set-up of how we gather intelligence in the future. It would have serious consequences," said the minister.

"We saw some of this stuff, but Tony saw it come across his desk virtually every day."

Robin Cook has intervened - claiming that he warned the government's dossier was curiously "derivative" when it was discussed at Cabinet.

"There was no hard intelligence of a current weapons programme that would represent a new and compelling threat to our interests," he said.

The row came in the wake of a visit by the prime minister to troops stationed inside Iraq.

Speaking in Basra on Thursday Blair praised the "wonderful achievement" of British troops.

He said UK troops had fought an "extraordinary" war and were engaged in a "remarkable" process of peace and reconstruction.

"You have brought tremendous honour on our country and respect and admiration everywhere for the way in which you did this," said the prime minister.

"I know this was real war with real bloodshed and real casualties.

"There are people you will know who aren't going back home, and we grieve for them and pay respect for everything they did and the sacrifice they made."