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The prime minister has said Britain, America and France will table a UN resolution on Syria's chemical weapons today.

However, I am told that the wording is still very much a work in progress.

Diplomats from the three allies are said to be discussing the questions of "what, where, when, who and how" - in other words what weapons should be removed from Syria, where should they be taken to, according to what timetable and who should supervise their removal and destruction.

There is also a discussion about what type of UN resolution should be tabled.

A so-called chapter 7 resolution is binding and is seen as authorising military action if other measures do not succeed.

The Russians have proved resistant to any such proposal. In the Kremlin they believe that the UN resolution which created a no-fly zone above Libya was exploited by Britain, France and America to allow the toppling of Colonel Gadaffi's regime.

They might prefer a resolution under the UN's Chapter 6 - entitled "Pacific Settlement of Disputes" - which stipulates that peaceful methods should be used to resolve disputes.

When David Cameron spoke to MPs he made clear his scepticism about Russia's intentions and revealed that President Putin had not raised the idea with him at the G20 summit last week.

He told MPs: "If we can achieve the removal and the destruction of the biggest chemical weapons arsenal in the world, that would be a significant step forward.

"So it is definitely worth exploring but we must be sceptical, we must be careful, we must enter this with a very hard head and some pretty cool calculations, because we do not want this to be some delaying tactic, some ruse to just buy time for a regime that must act on chemical weapons."

The Western allies have always wanted a UN process which either fails - allowing them to say that there is no choice but to take military action - or one that succeeds and specifically authorises it.