Mr Robin Cook has resigned from the British Cabinet as leader of the House of Commons,Downing Street announced.
The former Foreign Secretary indicated that he would step down if Britain joined the US-led attack on Iraq without securing a second UN resolution.
Mr Cook is due to make a personal statement to the Commons later this evening.
Foreign Secretary Jack Straw is also due to address MPs at 7.00 p.m., with theprospect of another ministerial resignation hanging over the government.
READ MORE
International Defence Secretary Clare Short has also threatened to quit over what she described as Mr Tony Blair's "reckless" handling of the Irq situation.