The BBC reported Thursday Blair discounts his senior political staff who no longer believe such weapons will turn up in Iraq.
They said such weapons did exist but were hidden or destroyed by Saddam Hussein before the war.
Meanwhile, former Prime Minister John Major called for an independent inquiry. He said he had backed the move to war because he had accepted the government's warnings but said "quite a few" of those alerts were now being questioned.
"It is essential that the word of government and the intelligence services is readily accepted by Parliament and the public," Major said.