He accepted that too many Iraqis were excluded by a programme to purge members of the ruling Ba’ath party, that the dissolution of the Iraqi army was botched and that the “biggest hole” in post-war planning was not to anticipate the possibility of an insurgency.

“The most consequential failure was to understand the tenacity of Saddam’s regime,” he said.

Wolfowitz, 69, a scholar at the American Enterprise Institute in Washington since he stepped down as World Bank president in 2007, has a somewhat diffident manner but he became animated as he reflected on the lead-up to the invasion and its aftermath.

He portrayed the Bush administration as deeply divided and he was fiercely critical of Colin Powell, the then secretary of state.

It was “outrageous” and “a joke” for Powell — who reportedly used to speak of a “Gestapo office” at the Pentagon — to have suggested that the case for the Iraq War was concocted by Wolfowitz and a cabal of fellow neoconservatives within the Bush administration, he said.

“I don’t think I ever met with the president alone. I didn’t meet with him very often. Powell had access to him whenever he wanted it. And if he was so sure it was a mistake why didn’t he say so?”