Today was the day that Gordon Brown had hoped would be his. To be shared perhaps with President Obama. They would be hailed as joint saviours of the world's financial system and joint guarantors of a global future. A bonus for the Prime Minister would be an afterglow of international achievement that would help redefine his premiership.
As the last of the national leaders arrived yesterday, however, the summit was starting to look a bit like the chaotic cavalcade simultaneously being played out in the capital's streets: by turns joyful and destructive; rehearsed and spontaneous; ridiculous and desperately serious. From America's first couple breakfasting at No 10, through the mutual compliments of the Brown-Obama press conference, to the US-Russia mini-summit which re-started the arms control process after almost 20 years – all punctuated by the protests in the City and rounded off , for the VIPs, by drinks with the Queen and a Downing Street dinner, where the last dots and commas of the communique were supposed to be finalised.
All this was predictable and, in its own way, scripted. Certainly not scripted, at least not from London, was the mid-afternoon press conference by the leaders of France and Germany. Their joint appearance might have been dismissed as a childlike squawk of "me too". But it was more than a plea to be noticed alongside the "big boys" from the US, China and Russia. It was a statement of principle and intent. President Sarkozy did not repeat his walk-out threat – a gesture clearly designed for domestic effect – but the message both he and Chancellor Merkel delivered was as specific as it was firm.
Saying they would speak with "one European voice", they demanded new international rules to govern hedge funds and tax havens, make commercial accounting transparent and regulate the pay of bankers and traders. M. Sarkozy said they were prepared to compromise, of course – "we make compromises in the EU every day"– but this had to be done with the involvement of all parties. Did he fear that the Franco-German demand for tougher regulation might be steamrollered at the 11th hour in favour of a vague agreement they would have rejected any earlier?
Mr Brown could be forgiven for thinking that France and Germany had contrived to rain on his parade. After all, what was apparently conceived as a grand US-British solution to an enveloping threat that they – or, in Mr Obama's case, his predecessor – had helped unleash, has become progressively less ambitious every week.
Its intended centrepiece – a globally coordinated fiscal stimulus that all participants would underwrite – has been replaced by an acceptance that in fiscal matters, national solutions will come first. Mr Obama may have warned that the US has no intention of becoming paymaster to the world. But Ms Merkel and M. Sarkozy made abundantly clear that they would not countenance anything that, in their view, would risk good money being thrown after bad.
The Franco-German intervention throws down the gauntlet to Mr Brown and Britain's chairmanship. At best, it will have precipitated much nocturnal redrafting; at worst, it risks a final communiqué even more diluted than the drafts already in circulation, or even – a prospect almost unthinkable – no significant agreement at all, either on fiscal stimulus or on regulation.
The outcome today could yet surprise. Nothing at such gatherings can be excluded, especially when the summit brings together as many divergent interests as this one and has been prepared against so fast-moving a backdrop. Yet it looks very much as though Gordon Brown's great hopes of laying the foundations of a new world order are destined to be cut down to size – and with it, his own political legacy.
But the last minute, and very public, démarche from the leaders of Europe's two biggest economies also casts the whole project for global economic management in a different light. The combination of a new and untried President in the White House, a rising China, a friendlier Russia and a more vocal Franco-German alliance marks a signal change. Yesterday, the United States and Britain seemed suddenly a little smaller, China a little bigger, and Continental Europe a force to be reckoned with.
By tonight, an agreed international plan of action along US-British lines might have shown this incipient redistribution of power to be illusory. Anything else, however, and we may be looking at the outlines of a very different future.