The move comes ahead of today's first report by Hans Blix, the UN inspections chief, on the first six weeks of inspections, which is expected to be inconclusive.
UN sources said last night that his report will describe Iraq's cooperation as a "mixed bag", strengthening the hand of sceptics who believe that the weapons inspectors need more time.
Britain and the US said yesterday that they were willing to allow the inspectors further weeks to complete their work, though they said this could not stretch on for months.
In the absence of the inspectors finding the "smoking gun", Britain and the US are working towards seeking a UN deadline of the end of February. Timing will depend on the inspectors' findings, the state of public opinion, military advice and European allies.
Britain is aiming to prevent the process from dragging on indefinitely, by handing over and publicising sensitive intelligence which allegedly shows that Iraq is flouting the UN.
Tony Blair said yesterday: "If Saddam fails to cooperate in being honest and he is pursuing a programme of concealment, that is every bit as much a breach as finding, for example, a missile or a chemical agent."
Colin Powell, the US secretary of state, underlined Washington's growing impatience yesterday, when he denounced Iraq's "evasions and lies" and declared that "time is running out".
"To those who say 'Why not give the inspections process more time', I ask: 'How much more time does Iraq need'?"
Despite the tough language, Washington made clear that it was still prepared to give the inspectors a limited period to continue their work.
Britain believes that it is up to Mr Blix to take the lead in certifying the level of cooperation, although the intelligence briefing is designed to sway public opinion and the security council that Iraqi compliance has been totally inadequate.
Examples cited by Whitehall, which are likely to be dismissed as propaganda by opponents of war, include the systematic dispersal around the country of chemical weapons munitions, long- range missile engines and planning documents.
The UN, including the sceptical French, Germans and Russians, are also being briefed that Iraqi scientists and their families are being threatened with punishment or death if they cooperate by giving interviews to inspectors.
It is also being alleged that Iraqi secret service operatives are conducting a highly elaborate spying operation on the inspectors' offices, hotel rooms and cars. Plans are also made by Iraqis to stage car crashes whenever inspectors approach a sensitive site in an attempt to delay them. Neverthless, it is also said that members of Saddam's inner sanctum are preparing to sell property and assets in preparation for taking flight.
The intelligence was released on the eve of Mr Blix's speech to the UN security council today.
Britain and the US now want the inspectors to keep a "steady check" on the level of cooperation with regular reports back to the council.
Speaking on BBC1's Breakfast with Frost, Mr Blair said: "They [the inspectors] have got to be given the time to do the job, but it is important to define what the job is.
"The job of the inspectors is to certify whether Saddam is cooperating or not with the UN inspections regime and that duty to cooperate doesn't just mean that he has to give them access to particular sites. It means he has got to cooperate fully in saying exactly what weapons material he has, allowing the inspectors to inspect it, monitor it and shut it down."
Asked whether that time should be weeks or months, Mr Blair said: "Well, I don't believe it will take them months to find out whether he is cooperating or not, but they should have whatever time they need."
Tariq Aziz, the Iraqi deputy prime minister, declared on Channel Four News last night that war was "not 100%" inevitable because of growing opposition in the US. His remarks coincided with a Newsweek/MSNBC poll showing that 66% of Americans think it is more important to allow more time.