A security council source said the UK was opting for a list that was "simple, striking and snappy" to win over wavering voters on the security council for a resolution that would set down a deadline for the tests.
The compromise, designed to break the deadlock gripping the UN security council and paralysing Washington's war plans, would see the deadline pushed back "by a few days" from the March 17 ultimatum proposed by London last week.
Last night's bout of frenzied diplomatic activity came hard on the heels of an unequivocal statement by President Jacques Chirac, who said France would veto any resolution authorising war. "Whatever happens, France will vote 'no'," President Chirac said in a joint interview with TF1 and France 2 television, on prime time television last night.
"War can only lead to the development of terrorism," he said. "The war will break up the international coalition against terrorism." The victors of any war would be "those who want a clash of civilisations, cultures and religions".
Russia also said yesterday that it would use its veto.
The compromise package proposed by Britain was also likely to fall on stony ground in Paris. While France might be prepared to contemplate a timetable for disarmament, it would veto any resolution which set an ultimatum.
The yawning gaps opening up in the security council led yesterday to an unprecedented statement by the secretary general, Kofi Annan, who warned the US that it would be in breach of the United Nations charter if it attacked Iraq without security council approval.
Mr Annan warned that military action without UN authorisation would raise questions. "The legitimacy and support of any such action will be seriously impaired," he said. "If the United States and others go outside the council and take military action, it will not be in conformity with the charter."
The UN charter forbids military action against other member states unless the action is in self-defence or condoned by the security council "to maintain or restore international peace and security".
Washington has argued that earlier security council resolutions were enough to provide the legal basis for an armed strike against Iraq.
The British government, which is in desperate need of UN backing, has been trying to balance Washington's impatience to go to war with the security council's reluctance to authorise military action.
London claims it has the support of the US for the revised plan. Furthermore, according to the British arithmetic, Angola, Cameroon, and Mexico are in favour and Guinea, Pakistan and Chile are also coming round.
Chile has proved to be one of the most awkward but it too is shifting towards the Anglo-US position, according to British sources.
Tony Blair phoned the Chilean president on Sunday to stress that the new resolution will take account of Chile's concerns.
Diplomats from the "middle six" members confirmed that they were holding discussions among themselves and were open to such a compromise.
The list demands that Iraqi scientists be taken abroad for interviews where they will be free from intimidation; the destruction of banned weapons; and the provision of documents explaining what had happened to the remainder.
The British ambassador to the UN, Sir Jeremy Greenstock, spent yesterday sounding out the undecided countries about their remaining concerns and then drew up the fresh set of proposals. If Sir Jeremy wins support for the new compromise, it could be put to a vote either tomorrow or Thursday.
Last night, he said Britain had not yet committed itself to benchmark tests but were seriously considering them as an option. "We are examining whether these tests will be a good idea and talking to our co-sponsors," he said.
US and British officials are also furious with the chief UN inspector, Hans Blix, for failing to mention evidence discovered by his inspectors of an undeclared drone aircraft and cluster bombs designed to scatter chemical and biological agents. The weapons were instead listed in a written UN working document and a last-minute addendum handed to council members after his verbal report last Friday.
But Mr Blix said last night: "Nowhere in the document is it asserted that Iraq has weapons of mass destruction. Everyone tries to squeeze us to get as much mileage as they can.