The inquiry into the Iraq war is set to be today told British and American leaders knew Saddam Hussein had no weapons of mass destruction as far back as 1998.

The UK’s ambassador to the United Nations at the time of the invasion in 2003, Sir Jeremy Greenstock, is today appearing before Sir John Chilcot’s inquiry in central London.

As well as being Britain’s representative at the UN from 1998 to 2003 he became the UK special representative for Iraq for the following year.

The allegation that the White House and Downing St always knew Saddam had no nuclear weapon capabilities or programmes formed the central part of Sir Jeremy’s memoirs that the Foreign and Commonwealth Office asked be withdrawn in 2005.

Yesterday the inquiry heard from the UK ambassador to Washington at the time of the Iraq war that the coalition search for a "smoking gun" had failed.

Sir Christopher Meyer told the inquiry that military preparations for the conflict had undermined UN weapons inspectors.

"And suddenly, because of that, the unforgiving nature of the military timetable, we found ourselves scrabbling for the smoking gun, which was another way of saying ‘it’s not that Saddam has to prove that he’s innocent, we’ve now bloody well got to try and prove that he’s guilty’," he said.

"And we – the Americans, the British – have never really recovered from that because of course there was no smoking gun."

The inquiry will continue to take evidence in public for a series of high profile figures, including military commanders and ministers, over the coming months culminating in the appearance of former prime minister Tony Blair sometime in the new year.