Two Foreign Office chiefs will be quizzed over one of the single most controversial issues of the Iraq War as the official inquiry into the conflict continues.

Sir William Ehrman and Tim Dowse, who were the heads of international security and counter proliferation respectively at the department in the run-up to the war, face questions over the threat from Iraqi weapons of mass destruction (WMDs).

A dossier published before the 2003 war contained the famous, but now discredited, claim that Saddam Hussein had WMDs that could be used within 45 minutes of an order being given.

On the inquiry's opening day in London, it emerged that British officials secretly discussed the prospects for "regime change" in Iraq in late 2001 - more than a year before the invasion. Inquiry chairman Sir John Chilcot heard that Foreign and Commonwealth Office (FCO) officials drew up an internal "options" paper which included the possibility of ousting Saddam Hussein.

However, Sir William Patey, the then head of the FCO's Middle East department, said the idea had been swiftly rejected on the grounds that there was "no basis in law" for such action. The inquiry heard that a two-page paper was drawn up against a background of growing impatience in the United States with the strategy of "containment" of Saddam.

The international sanctions regime was "in trouble", while there were increasing concerns that Saddam was making progress in his efforts to acquire WMDs.

Sir William said: "This is a paper I commissioned from my staff and said, 'Come on, let's have the whole range of options out here. Nothing's off the table'."

He added: "It was very much an internal paper. We didn't go into how to achieve regime change."

The inquiry also heard that even in early 2001, elements of the new US administration of President George Bush were already discussing the possibility of "regime change" in Iraq.