Three of the men are among the 55 that the coalition forces have declared the most-wanted of the regime, including the leaders of military intelligence and the chief of air defence.

"They're collapsing like a house of cards," said Lieutenant-Colonel Tom Kurasiewicz, a Pentagon spokesman. General Zuhayr Talib Abd al-Sattar al-Naqib, who headed military intelligence, surrendered to US forces in Baghdad, a defence official said. Another US official said the general had headed the directorate of military intelligence since 2002.

Also in US custody are Muzahim Sa'b Hassan al-Tikriti, air defence force commander and No 10 on the US military's list of wanted Iraqis, and Muhammad Mahdi al-Salih, the Iraqi minister of trade and No 48 on the list.

The defence secretary, Geoff Hoon, said he believed Sad dam was probably still hiding in Iraq. "In the end we don't know, but it is still our best judgment that he is [in Iraq]," he said during a visit to British troops in the south of the country.

"As each day goes by, as we continue to search those places he may be hiding, we have to keep an open mind - but it is still my best judgment," he said.

His comments reflect the best guess of the British intelligence agencies, which question Washington's view that Saddam was killed when four bunker-busing bombs were dropped on a building attached to a restaurant in the wealthy Mansour district of Baghdad.

Mr Hoon also said yesterday that he was confident that evidence of Iraq's programme of weapons of mass destruction would eventually emerge. Mr Hoon was visiting British troops in the port of Umm Qasr, where humanitarian aid is now being delivered, and Basra, Iraq's second biggest city.

· The chief of defence staff, Admiral Sir Michael Boyce, is to retire next week, and will be succeeded by General Sir Michael Walker, currently the army chief of staff, it was announced yesterday.