For more than a decade, London's Docklands, with its glass and steel skyscrapers, was the pulsating heart of global financial capitalism, the East End postcode with a Wild West atmosphere, where interfering politicians feared to tread. In 11 days' time, 20 of the world's most important leaders will gather here, at the ExCeL Centre, with a mandate to clear up the chaos unleashed by the crunch - and rein in the might of the financiers.
Gordon Brown has trumpeted the London summit as nothing less than a New Deal for the world's crisis-hit economy; one day that will rewrite the rules of financial markets, fix the broken banking system and pull the world back from a new Great Depression.
Last week, the International Monetary Fund warned the stakes could not be higher: for the first time since 1945, the global economy as a whole will contract in 2009. "Turning around global growth will depend critically on more concerted policy actions to stabilise financial conditions, as well as sustained strong policy support to bolster demand," the IMF said. The fund sees the current crisis as the most serious since the 1930s, when the US economy contracted by 25% in four years and six million unemployed in Germany led to the rise of Hitler.
The devastation of the Great Depression and the ravages of the second world war led to the most radical shake-up of the world's economic system since the industrial revolution. In 1944, the historic Bretton Woods summit created the system of fixed exchange rates that lasted until the 1970s, and the IMF and World Bank, which remain guardians of the global economy today.
In the autumn, the government was hailing the London summit as a 21st-century Bretton Woods, yet Downing Street has already begun rowing back from the early fanfare about rebuilding capitalism - and judging by the communiqué from G20 finance ministers after their summit in Horsham, West Sussex on 14 March, ambitions are now relatively modest.
"They're just not tackling the problem of how much of the casino needs to be shut down," says Heiner Flassbeck of Unctad, the UN's trade and development arm, which published a scathing report last week calling for G20 ministers to overturn two decades of "market fundamentalist laissez-faire". Flassbeck said the sub-prime mortgages that triggered the crisis were only one symptom of an out-of-control financial sector; there had also been rampant speculation in markets for commodities, currencies and other assets, which must now be re-regulated. "Because all these pyramids have collapsed in a very short time, that's why we have seen such a global impact."
An early warning that next month's meeting might not meet Brown's grand expectations came when he clashed with other G8 countries, including Italy, about whether it should be called a "G20 summit" at all - hence its official title of the London summit. (This despite unfortunate associations with the ill-fated 1933 London summit of world leaders, which was torpedoed by Franklin Roosevelt, a Democrat president newly arrived in the White House with a mandate to revive a US economy deep in slump.)
Signs of potential conflict abound: Barack Obama wants the summit to focus on measures that can be taken now to revive growth and create jobs, and will be armed by the latest emergency steps taken by the Federal Reserve to pump trillions of dollars into the US economy. The Europeans worry that policymakers are doing too much in the short term to boost demand and too little in the long term to ensure there is no return to the bubble conditions that created the current crisis. But calls from Nicolas Sarkozy and Angela Merkel for curbs on hedge funds and private equity companies, together with tougher regulations on "toxic" derivative products may be greeted coolly by the Americans.
Alistair Darling tried valiantly to paper over the cracks at last weekend's meeting in Horsham. Policymakers pledged to do "whatever it takes", for as long as it takes, to lift the world economy out of recession, while acknowledging that many governments have already taken steps; but back in London, Merkel was reminding Brown that any decisions Germany might take to launch a further fiscal stimulus would be a matter for its parliament in Berlin, not for an international summit.
"Leaders talk global, think national," says Gerard Lyons, chief economist at Standard Chartered, though he adds that the lack of substantive proposals after the finance ministers' meeting could mean they are saving the goodies for their bosses.
The chemistry between the G20 leaders is hardly warm. Brown spent a decade as chancellor lecturing his continental counterparts about Britain's deregulated financial markets and flexible labour market, and they are determined not to let the prime minister claim credit for saving the world, especially when Britain is going to have one of the deepest recessions. Forecasts presented to G20 governments by the IMF last week showed UK GDP declining by 3.8% this year and a further 0.2% in 2010.
In the US, meanwhile, Obama is struggling to complete his financial team, with Treasury secretary Tim Geithner the only major post at the department confirmed. Geithner, who scraped through his confirmation on Capitol Hill after admitting failing to pay $34,000 in taxes, has since been battered by the political storm over bonuses paid to executives at AIG, and Wall Street's initial lack of confidence in his rescue package.
Expectations for what the leaders should achieve are still running high. A mass rally, involving a coalition of more than 100 groups, from churches to trades unions, is planned for next Saturday. Under the banner of "Jobs, Justice and Climate", thousands will march through central London to a rally in Hyde Park, calling for Brown and his fellow leaders to reform international markets, protect vulnerable jobs and support the world's poor through the credit crunch.
On 2 April though, a security lockdown will be in place. Police are on high alert lest the first summit of world leaders to be held in London since John Major hosted the G7 in 1991 become a pitched battle between the security forces and anti-globalisation protesters.
With the leaders of rich countries facing intense pressure at home to combat mass unemployment and shore up their embattled financial systems, campaigners are nervous that there will be little will for fresh efforts to help the poor.
Ngozi Okonjo-Iweala, managing director of the World Bank and a former Nigerian finance minister, says more than 50 million people are likely to be plunged into poverty by the credit crunch, as developing countries are starved of resources and volatile commodity prices wreak havoc on exporting countries' public finances. "The story that needs emphasising is how the emerging countries have been impacted by the second and third rounds of the crisis," she says. "The fact is that developing countries should be part of the solution: they did not cause the problem."
Simon Maxwell, director of the Overseas Development Institute, says: "If Gordon Brown had his way, extra money would be found. He has provided extraordinary leadership in keeping development high on the agenda. Other countries are much less willing to take development seriously. Some are saying, 'Don't ask us, because we don't want to embarrass you by saying no'."
However, the fact that the G20, rather than the G8, is the forum for these discussions is a recognition of the changing global economy. For decades after the second world war, the leading capitalist economies of western Europe, North America and Japan dominated the scene. They accounted for the lion's share of global output and trade and controlled the IMF and World Bank, promulgating a controversial set of free market policies known as the "Washington consensus".
When modern summitry began in the mid-1970s, it involved only six countries - the US, West Germany, Italy, Japan, France and Britain - but the G6 quickly became a G7 with the arrival of Canada. Boris Yeltsin was rewarded for his role in turning Russia into a market economy when he was given a seat in the 1990s, but in recent years the limitations of the G8 have been exposed. Attempts to discuss currencies and the global economic imbalances have been rendered futile by the absence of China and the oil exporters; the input of China and India have been deemed vital if there is to be progress on climate change; China, India, Brazil and South Africa are all key players in the long-running Doha round of trade talks.
Reluctant to cede power and influence, the G8 first came up with an uneasy compromise. It invited five leading developing countries - China, India, Brazil, South Africa and Mexico - to some sessions of the annual summer summit. This G8-plus-5 format, predictably, ruffled feathers in Beijing and New Delhi, and matters came to a head in Japan last year when the top-level Chinese delegation took great offence at being kept waiting for an hour in Hokkaido while the G8 wrapped up private business.
So, when George Bush called a crisis meeting after last autumn's financial meltdown, it was clear that the format had to be wider than the G8. It included all five big developing countries together with Indonesia, the world's fourth most populous country, Saudi Arabia, the biggest oil producer, Argentina, Turkey, Korea and Australia - and the EU took the 20th seat around the table.
While broader and more representative than the G8, the G20 has its critics. Some doubt if a body so diverse can come to any agreement, pointing out that it was hard enough to reach consensus at the G8. Others argue it still excludes the very poorest countries of sub-Saharan Africa - though Downing Street has invited Ethiopia, representing Nepad, the African development coalition, Gabon's foreign minister Jean Ping from the African Union, and Donald Kaberuka, president of the African Development Bank.
Leaders are expected to promise measures to tackle the immediate crisis, including more resources for the IMF to lend to struggling economies, and help for poor countries unable to finance international trade because of the credit crunch. Amar Bhattacharya of the G24 Secretariat, which represents low-income countries, says he is encouraged by the progress already made, but it will be crucial to ensure that any promises - on new fiscal stimulus, for example - are carefully monitored: "I think the best way to proceed is to have a very effective monitoring system, so that we can ensure that those locomotives with the most steam are doing the most work."
The G20 leaders will also discuss how to regulate international financial markets more effectively, to prevent a crisis on the extraordinary scale of the past two years from happening again. Hedge funds are likely to find themselves facing a stricter regime after 2 April, though details remain sketchy - the finance ministers merely called on them to be more transparent in reporting their positions. Complex assets such as derivatives, and the off-balance-sheet vehicles used by many credit-crunched banks, are also expected to come under closer scrutiny.
All G20 leaders also agree something may be needed to rein in the activities of tax havens, not just to stop government revenues being lost, but to throw open the complex and secretive dealings of multinational financial institutions that have used offshore locations to conceal parts of their business from regulators.
However, with several of the most notorious tax havens, including Liechtenstein and Jersey, making grand declarations about their new commitment to openness, there are fears that the will to take tougher action may be absent. Claire Melamed, director of policy at Action Aid, says: "It would be a major missed opportunity if they don't follow through. At the moment, there are quite worrying signs they're not going to."
For Brown, much more is at stake than creating international common purpose in the face of economic disaster. The London summit is one of two meticulously planned political moments for Labour to show that, despite Britain's role as home of some of the worst-regulated and hardest-hit financial institutions, the government is part of the solution, not the author of the crisis. Little more than a fortnight after the summit, Darling hopes to use his budget as a new assault on the worsening recession and lengthening dole queues.
In October, when Britain's bank recapitalisation plan looked firmer and more decisive than US treasury secretary Hank Paulson's flailing response to the woes of Wall Street, Brown saw his popularity bounce, as he bestrode the world scene. But with 2 million now unemployed at home, it may take more than even the most successful summit to restore his electoral fortunes.
So determined is the government to win the favour of the leaders flying into Docklands that it has passed special legislation to suspend the smoking ban in the vicinity of the ExCeL centre for the duration. But it may take more than a grand international bargain struck in the nostalgic surroundings of a smoke-filled room to save the world economy - or resuscitate the Brown premiership.
Larry Elliott looks at nearly 500 years of key political gatherings
The field of the cloth of gold
The first summit the modern age would recognise as such took place in the summer of 1520 just outside Calais, when Henry VIII crossed the Channel for talks with Francis I. Although it lacked TV cameras and spin doctors, the Cloth of Gold had all the classic features of summitry; it was orchestrated by top officials; it involved more pageantry and feasting than substance; and the show of amity did little to paper over the cracks in the fragile relationship between the two countries.
The treaty of Versailles
Two months after the end of the first world war, the Allied Powers gathered at Versailles in January 1919. A mixture of the idealistic plans for a League of Nations and the self-determination of peoples proposed by the US President Woodrow Wilson and the desire for recompense for the damage to France from the devastation on the western front, the conference saddled a dismembered Germany with a massive reparations bill. John Maynard Keynes, part of the UK delegation, warned in his Economic Consequences of the Peace that Versailles was storing up problems for the future.
Bretton Woods
A quarter of a century later an ailing Keynes had the opportunity to do better, second time round. Two-and-a-half years in the planning, the three weeks of talks at the Mount Washington hotel in New Hampshire in July 1944 were dominated by Keynes, but the real decisions were taken by his American counterpart, Harry Dexter White. Bretton Woods created the International Monetary Fund to oversee a post-second world war system of fixed exchange rates, and the World Bank to help to rebuild the economies of western Europe, but plans for a World Trade Organisation were put on ice for half a century following opposition from the US Congress.
Rambouillet
Three decades of prosperity came to an end with the oil shock of 1973-74. The combination of rising unemployment and inflation - stagflation - prompted the French President Giscard D'Estaing to invite five other world leaders for a "fireside chat" at a château just outside Paris. Although modest by later standards, this was the first of the gatherings of world leaders which now take place on a rotating basis each year. Rambouillet had no easy answers to the first recession in the west since the 1930s, but its main themes - avoiding protectionism, energy dependency and boosting growth - will be on the agenda next week.
Gleneagles
The last big summit of world leaders to be held on British soil, the meeting at the Scottish luxury hotel in July 2005 coincided with - and to an extent was overshadowed by - the 7/7 terrorist bombings in London. Tony Blair shuttled between the summit and Downing Street and, after much arm-twisting, persuaded the G8 to sign up to a package for developing countries that involved debt relief, a £50bn increase in aid and easier access to western markets. Although Gleneagles was one of only a handful of summits to result in more than a bland communiqué, the G8 has yet to deliver on its promises.