UN weapons inspectors yesterday uncovered a cache of empty chemical warheads in Iraq which were not mentioned in Saddam Hussein's supposedly complete declaration of his weapons of mass destruction programmes.

The inspectors said the warheads, discovered at an ammunition storage area in southern Iraq, were in "excellent condition".

Iraqi officials dismissed the find as a "storm in a teacup", insisting that the warheads were old artillery mentioned in its 12,000 page December declaration.

Prime Minister Tony Blair, who will meet UN chief weapons inspector Hans Blix at Chequers today, was informed of the discovery while on a short visit to Scotland.

It will be up to the UN Security Council to determine whether the find amounts to a breach of UN resolutions - potentially bringing military action against Saddam Hussein a significant step closer.

A Downing Street spokes-man said: "We note what the spokesman for the UN weapons inspectors has said about their find. We await more information."

In Washington, White House spokesman Ari Fleischer said the US administration was assessing the information.

Sir Jeremy Greenstock, Britain's ambassador to the UN, told journalists: "I want to hear the inspectors' report on this before I make any judgement. It sounds as though it is interesting news."

Foreign Office minister Mike O'Brien said: "We are going to have to evaluate the information, but we have always said that Saddam has been concealing things. "

The warheads were found during a visit by inspectors to the Ukhaider ammunition storage area, 75 miles south of Baghdad.

Last week, Mr Blix told the UN Security Council that inspectors had yet to uncover any "smoking guns" during their search for weapons of mass destruction.

But yesterday's discovery would appear to be the closest thing yet to such damning evidence.