Tony Blair has told MPs "we are entering the final phase of a 12-year history of the disarmament of Iraq".

The UK prime minister said that a second UN resolution should be passed unless Iraq cooperates fully with the weapons inspectors.

"I continue to believe the UN is the right way to proceed," he said.

He and US President George Bush had agreed on this "provided, as ever, that seeking such a resolution is a way of resolving the issue not delaying or avoiding dealing with it at all".

I do believe that it is possible to halt the march to war

Click here to read about Tony Benn's Iraq visit

But the prime minister warned that there was no way the US and Britain would back down over Iraq disarming.

"Show weakness now and no one will ever believe us when we try to show strength in the future," he said.

Tory leader Iain Duncan Smith told MPs: "If the international community backs away from dealing with Saddam Hussein now, this will be seen as a green light for every rogue state and terrorist group around the world."

Saddam confident

But the prime minister knows that he has a battle on his hands not just to convince the British public of his case for war but in order to win over many of his own backbenchers.

Within hours of Mr Blair's statement a group of actors from the National Theatre including Ralph Fiennes and Corin Redgrave mounted a demonstration against war with Iraq on the south bank of the River Thames.

In the Commons there was particular concern at the thought of military action without a fresh UN resolution.

Tony Blair insists George Bush is willing to go through the UN

Liberal Democrat leader Charles Kennedy warned that government still had to make a "credible case" for war.

A US dossier claiming to expose Iraq's deliberate weapons concealment has bolstered Mr Blair's suggestion that he can win over sceptics.

And Downing Street has published its own report detailing ways, the government claims, that Iraq has been deliberately obstructing the weapons inspectors.

Among its main points are:

• The Iraqi regime is trying to hide documents and materials in places where they are unlikely to be found, such as private homes of low-level officials, universities, hospitals and even mosques.

• Iraqi intelligence officials outnumber the inspectors by 200:1 and spy on them around the clock.

• They also bug the rooms where the inspectors interview Iraqi scientists. The interviewees realise this and therefore do not give away any information for fear of reprisals.

• Spies posing as guards, drivers and escorts tip off the authorities about where the inspectors are heading to, so reducing the element of surprise in the inspections.

• If the inspectors do change course, a special team organises a car crash to delay them.

However, Saddam Hussein is said to be optimistic about avoiding war, according to former Labour cabinet minister Tony Benn who travelled to Iraq to interview the president.

Meanwhile, front-line British soldiers have started to arrive in Kuwait bringing their number to more than 1,000 with the build-up continuing later this week.

United Nations?

Following the talks with Mr Blair, the US president warned that he would not tolerate delay on acting against Iraq.

The UK prime minister's strategy has been to maintain that the US president is willing to work through the UN.

But support for action is by no means guaranteed.

Among the European nations concern has been voiced about military action against Iraq most notably by France and Germany.

Mr Blair has briefed French President Jacques Chirac on his talks with Mr Bush, in advance of Tuesday's Anglo-French summit in Le Touquet.

Clock ticking

France's support is vital as it has a veto in the UN security council and could break a resolution against Iraq.

Chief UN weapons and nuclear inspectors Hans Blix and Mohamed El Baradei are to return to Baghdad for talks.

Meanwhile the British troops arriving in Kuwait, alongside the growing US military presence in the region, have included combat soldiers from 3 Commando Brigade of the Royal Marines.

Military officials are not saying how many of them have arrived so far, but they are saying that a further 200 or so will fly in on Monday and a full commando unit of several hundred will be in place within the next few days.

The government will also announce the deployment of RAF personnel to the Gulf later in the week.

It is believed another 60 aircraft will join the 21 already in the region.