The government has withdrawn its much vaunted claim that Iraq could launch weapons of mass destruction in 45 minutes.

But Jack Straw told MPs that he stood by the decision to launch the conflict, saying: "I still believe it was the correct decision."

The foreign secretary confirmed the chief of the Secret Intelligence Service had written to parliament's intelligence and security committee "formally withdrawing" the claim.

Responding to that news, Sir Menzies Campbell of the Liberal Democrats said the "building blocks of the government's case for military action are crumbling before our eyes".

"The withdrawal of the 45 minute claim drives a horse and cart through government credibility," he added.

But Straw argued that the Iraq Survey Group's conclusions last week provided "chapter and verse" on Saddam Hussein's intent to develop chemical and biological weapons and use them as he had done in the past.

He also said the report showed Saddam was a current threat to the region and world despite the absence of an arsenal.

Conservative spokesman Gary Streeter said Straw had not gone far enough.

"The British people must get a full apology and a full explanation," he said.