The huge sum, equivalent to £548,000,000,000, was revealed as the US held secret meetings with rebels to end the fighting.

The cost of the war, post-war efforts and the loss of world output due to rising oil prices will hit $1.25trillion by 2010, it has been estimated.

Prof Keith Hartley, director of the University of York's Centre for Defence Economics, believes it would have been cheaper to pay off Saddam Hussein to achieve regime change.

He said: "If at the outset the Americans anticipated the Iraq operation would cost $100 billion, they could have given Saddam and his family $20billion to go, $50billion to Iraq and still have had $30billion left over.

"The UK would not have been involved, no-one would have died and no buildings would have been destroyed."

Economic expert Prof Hartley says the cost to Britain could top £5billion by the end of next year - over £1billion more than forecast.

Meanwhile details were revealed yesterday of a secret meeting between rebels, US Army officials and secret agents on June 3 in Balad, 40 miles north of Baghdad.

One of the few groups in Iraq not to attend was Abu Musab al-Zarqawi's gang which killed British engineer Ken Bigley. It is the first sign the US is prepared to enter talks with terrorists to end the killings.

Yesterday US defence secretary Donald Rumsfeld admitted the insurgency in Iraq could go on for another 12 years.

Addressing a question about whether US troops levels are adequate to vanquish the increasingly violent resistance, he said: "We're not going to win against the insurgency. The Iraqi people are going to win against the insurgency. That insurgency could go on for any number of years. Insurgencies tend to go on five, six, eight, 10, 12 years."

An upsurge in suicide bombs in Iraq has forced Britain and America to pledge not to suddenly pull out of Iraq.

More than 30 Iraqis died yesterday - half of them police officers - in three separate suicide bomb raids around the northern city of Mosul.

Today Tony Blair holds talks with Iraq's interim President Ayad Allawi at No10.