Tony Blair was “duped” by George Bush into backing the Iraq war, Gordon Brown has claimed.

Mr Brown, who was Chancellor of the Exchequer at the time, said the US failed to disclose a report showing that there was no evidence that Saddam Hussein had access to weapons of mass destruction.

The secret report also fatally undermined Britain’s so-called “dodgy dossier” which claimed that Iraq could launch a biological attack on Britain within 45 minutes, the Mirror reported.

“We were all misled on the existence of WMDs,” Mr Brown has written in his new book, My Life, Our Times, which is being published on Tuesday.

“Given Iraq had no usable chemical, biological or nuclear weapons that it could deploy and was not about to attack the coalition, then two tests of a just war were not met.

“War could not be justified as a last resort and invasion cannot now be seen as a proportionate response.”

The Bush administration nurtured doubts about Mr Brown. In August 2010 the Sunday Telegraph disclosed that Tony Blair was urged by Washington to prolong his time in office rather than hand the reins over to Gordon Brown.