Foreign Secretary Jack Straw last night acknowledged that Britain may have to abandon hopes of securing a new United Nations resolution before going to war with Iraq.

At a news conference at the Foreign Office, he repeatedly refused to say whether the draft resolution tabled by Britain, the US and Spain would be put to a vote in the Security Council.

Earlier, his Spanish counterpart Ana Palacio openly accepted that the resolution may be withdrawn, citing the threat by President Jacques Chirac to wield the French veto "whatever the circumstances".

The acceptance that the resolution may have to be dropped will have come as a bitter blow to Tony Blair, who desperately needs a new UN mandate for war if he is to avoid a potentially catastrophic split in the Labour Party.

Earlier, at Prime Minister's Questions, Mr Blair assured MPs he still intended to put the resolution to a vote in the Security Council.

He even announced a series of six "benchmarks" against which Iraqi compliance with UN demands to disarm could be judged in a final attempt to win round the undecided council members. The benchmarks were:

* A public statement by Saddam Hussein admitting possession of weapons of mass destruction and stating his regime had decided to give them up;

* A commitment to allow Iraqi scientists to be interviewed outside Iraq;

* Surrender of and explanation of stocks of anthrax;

* Commitment to destruction of proscribed missiles;

* Account for unmanned drone aircraft;

* Commitment to surrender all mobile bio-production laboratories.

But later, Mr Straw refused to guarantee that there would be a vote on a new resolution before military action was launched.

"What I guarantee is that we are working as hard as we possibly can to secure a second resolution," he said.

Britain and the US have been working frantically to get the nine votes they need to secure a resolution in the hope of putting pressure on France and Russia not to use their vetoes.

However, it would appear they may have decided that they are better off going to war without a new resolution, rather than seeing their proposed draft rejected by the Security Council.

Mr Straw said, one way or the other, the process of trying to find a resolution would be concluded by the end of the week.

In the Commons, Mr Blair made clear that British troops would be fighting alongside the Americans, despite US Defence Secretary Donald Rumsfeld's suggestion that the US could "go it alone" if the Government failed to get Parliamentary approval for military action.

"I am determined we hold firm to the course we have set out," he said.