The Government was warned just days before the invasion of Iraq that Saddam Hussein may be unable to use his chemical weapons, the official inquiry into the war has been told.

The evidence on Iraq's supposed weapons of mass destruction (WMD) emerged on the second day of public hearings in London.

Senior Foreign Office officials said ministers were repeatedly warned the intelligence on Iraq's supposed WMD was "patchy", even though then-PM Tony Blair told Parliament that they represented a "clear and present" threat.

The officials said intelligence was received in March 2003 suggesting Saddam had "disassembled" his chemical weapons and had not given the order to re-assemble them.

Sir William Ehrman, who was director of international security at the Foreign Office, said reports to ministers by the Joint Intelligence Committee had made clear just how uncertain the intelligence was. In April 2000 the picture was described as "limited to chemical weapons", in May 2001 the knowledge of WMD and ballistic missile programmes was "patchy", in March 2002 the intelligence was "sporadic and patchy".

In August 2002 a briefing noted that "we know very little" about Iraq's chemical and biological weapons work since late 1998, and in September 2002 the intelligence "remained limited".

With British and US troops massed on the Iraq border and the invasion just days away, he said evidence had come in that his weapons might not be usable at all.

"We did, I think on March 10, get a report that chemical weapons might have remained disassembled and Saddam hadn't yet ordered their assembly," he said. "There was also a suggestion that Iraq might lack warheads capable of effective dispersal of agents."

However, Sir William insisted that it had not made any difference to the case for war as it simply proved that Saddam was not co-operating with the United Nations weapons inspectors.

"I don't think it invalidated the point about the programmes he had. It was more about use," he said. "From the counter-proliferation point of view it just proved that he had been lying and that he had prohibited items."