Critics of the government's Iraq dossier need to provide evidence of foul play, Tony Blair has said.

Responding to criticism from the leader of the Liberal Democrats, the prime minister stood by his firm line that the government had not made exaggerated claims of the Iraqi threat.

Speaking in the Commons on Wednesday, he challenged opponents of the war to back up their claims of wrong-doing with proof that Downing Street communications chief Alastair Campbell doctored the Iraq dossiers.

Charles Kennedy had earlier said that evidence given to the foreign affairs committee by Campbell and foreign secretary Jack Straw had been inconsistent.

The Lib Dem leader said that there were disparities in the evidence given to the foreign affairs committee by the two men over when the infamous 45-minute weapons launch claim was inserted into the first Iraq dossier.

"Can the prime minister make clear once and for all which version is right?" Kennedy asked.

Blair rejected the demand and described the charge that the dossier had been exaggerated as "completely and totally untrue".

"If anyone actually has any evidence let them produce it," Blair told MPs.

Meanwhile, media reports suggest that the foreign affairs committee, currently investigating the issue, is likely to split along party political lines over the issue when it reports.