David Cameron on Monday evening made a final attempt to bounce Russia into supporting a future for Syria without President Bashar al-Assad.
The Prime Minister lined up the support of the six other members of the G8 nations for a five-point plan to underpin a second round of peace talks on Syria in Geneva. At a working dinner at the G8 summit at Lough Erne, Northern Ireland, he challenged Russia's Vladimir Putin to join the rest of the eight-member club or face isolation. "It is a clarifying moment," said a British source.
Mr Cameron hopes his five principles will be reflected in the G8's communiqué when the two-day summit ends on Tuesday - with or without Russian support. He made clear on Monday night that the other seven members could issue their own statement on Syria, formally isolating President Putin on the world stage.
Despite the war of words over Syria between Russia and the West as they line up on different sides in the bloody civil warm, the Prime Minister believes there is more common ground with Russia than meets the eye. His principles are:
* a transitional government with executive authority in Syria, which means without President Assad
* condemning the use of chemical weapons anywhere in the world
* a drive to improve humanitarian relief to the Syrian people and resolve access problems for aid agencies trying to reach them
* a pledge to combat extremist groups wherever they operate
* learning lessons from Libya by planning in advance for "day one" of a new Syria.
The Prime Minister hopes to shift the spotlight from war in Syria to peace talks. But there are clear signs that President Putin was angered by the Obama administration's decision last week to offer direct military support to the anti-Assad rebels. On Monday Russia said it would not permit no-fly zones - one of the possible options - to be imposed over Syria. "I think we fundamentally would not allow this scenario," said Alexander Lukashevich, its Foreign Ministry spokesman.
Stephen Harper, the Canadian Prime Minister, admitted it would be hard to secure President Putin's support. "We are not, unless there is a big shift in position on his part, going to get a common position with him at the G8," he said.
President Assad warned a German newspaper that European nations backing the rebels would "pay the price" if they joined those sending weapons to Syria.
Presidents Obama and Putin met for crucial one-to-one talks in the margins of the G8 summit, before the eight leaders sat down for a dinner of crab, prawn and avocado salad, local beef and apple crumble with Bushmills whisky custard.
Mr Cameron appeared to have a better chance of success when he proposed a joint declaration by the group of eight that they would not pay ransoms to terrorist kidnappers. In the past, only Britain, the United States and Canada have declared that they would not pay up and France, Italy and Japan are reported to have been willing to hand over ransom money.
The Prime Minister will tell the summit on Tuesday that ransoms are now the biggest single source of terrorists' funds, and that the international community needs to stand together to choke off the supply. Al-Qa'ida has raised an estimated $70million (£45million) in the past three years from ransoms, including Euros 33 million (£28million) in the Maghreb, with an average payment of $2.5million (£1.6million) for each hostage.
Before Syria dominated the G8's discussion of world affairs on Monday evening, Mr Cameron, in a round of media interviews, argued that Britain had a duty to "engage" despite growing domestic opposition to the prospect of arming the anti-Assad forces.
Boris Johnson, the Mayor of London, said the UK would have no way of preventing weapons reaching "al-Qa'ida-affliated thugs" if it supplied the rebels following the EU's decision to lift its arms embargo. "This is not the moment to send more arms. This is the moment for a total ceasefire, an end to the madness."
But William Hague, the Foreign Secretary, said Britain must prevent the Syrian opposition from being "exterminated". He told BBC Radio 4: "Our fear is we are only going to get a political solution to this crisis if the opposition, the moderate sensible parts of the opposition, can't be destroyed. Therefore, they do need assistance of various kinds."
The White House confirmed last night that the US would provide another $300m (£190m) in aid for refugees affected by the Syrian civil war