The president’s daily brief (PDB) was the highly classified report of the most sensitive and supposedly important intelligence developments overnight. Only George W Bush and his inner court of top officials received it.

It was late July 2003. Iraq was firmly in American and British hands after the brief war in March to topple Saddam Hussein. The organised insurrection had not yet broken out, but there were two big problems: anarchy and the hunt for Saddam’s weapons of mass destruction — the official pretext for the invasion.

Kay, one of the world’s foremost experts on nuclear weapons inspections, had been in charge of the hunt for WMD for only a few weeks and was already coming to the conclusion that he might not find stockpiles anywhere in Iraq.

Bush and Vice-President Dick Cheney were waiting in the Oval Office next morning to hear about Iraq. Kay delivered his bombshell: he thought the Iraqis might have had the equipment, the facilities and the material to make WMD on short notice but they might not have actually produced any. The response surprised him.

“Keep at it,” Bush said. “You understand you’re to find out the truth about the programme. What do you need that we can do for you?” “Sir, the only thing we need right now is time and patience,” Kay said.

“You have the time. I have the patience.”

Kay left the meeting almost shocked at Bush’s lack of inquisitiveness.

“He trusted me more than I trusted me,” Kay later recalled. “If the positions had been reversed, and this is primarily personality, I think, I would have probed. I would have asked. I would have said, ‘What have you done? What haven’t you done? Why haven’t you done it?’ You know, ‘Are you getting the support out of DOD (department of defence)?’ The soft spots. Didn’t do it.”

On the way out Cheney and Scooter Libby, his chief of staff, pulled Kay aside. Libby had a small sheaf of intelligence reports, including some sensitive, raw National Security Agency (NSA) communications intercepts. As with many intercepts, they were maddeningly vague. They had interesting little tidbits, and sometimes even specific locations were mentioned, but it was as clear as smoke. Kay was astounded that the vice-president of the United States was using such raw intelligence. Cheney and Libby were acting like a couple of junior analysts, poring over fragments as if they were trying to decipher the Da Vinci Code.

He was not the first American WMD-hunter to suspect that there might not be anything there. The general tasked with finding the hidden weapons programme had reached the same conclusion months before the war even started.

Back in September 2002, six months before the war, Major General James “Spider” Marks was given the assignment of a lifetime: top intelligence officer for the US-led forces planning to invade Iraq. It was his job to find the WMD as the troops went in.

Cheney had recently given a speech that Marks believed must have been cleared by US intelligence. “Simply stated, there is no doubt that Saddam Hussein now has weapons of mass destruction,” Cheney had said. “There is no doubt that he is amassing them to use against our friends, against our allies and against us.”