Basking in the compliments of fellow world leaders, the Prime Minister said the package – alongside a global fiscal stimulus worth $5 trillion by the end of next year – would double world growth to 4 per cent by 2010.
The markets seemed to agree, with the FTSE 100 closing up 4.3 per cent, taking it above 4,000 points for the first time since February. Stock markets in Frankfurt and Paris also made gains, and in New York the Dow Jones closed up 2.8 per cent at 7,978.08.
"This is the day the world came together to fight back against the global recession," Mr Brown said. "There are no quick fixes but, in the six pledges we make today, we can shorten the recession and we can save jobs."
However, last night ministers were forced to play down suggestions Britain would need a bail-out from the International Monetary Fund after Lord Mandelson, the Business Secretary, said the UK would not be "first in the queue" for such assistance.
US President Barack Obama said that the agreement marked "a turning point in our pursuit of global economic recovery".
Asked if the measures were enough to end the recession, he said: "In life, there are no guarantees. In economics, there are no guarantees… there are always risks involved. I have no doubt, though, that the steps that have been taken are critical for preventing us from sliding into a depression."
He added: "I think the patient has stabilised. There are still wounds that have to heal. There are still emergencies that can arise."
The $1.1 trillion (678 billion) deal will focus on boosting the reserves of the International Monetary Fund to free up extra lending for developing economies, such as Brazil and Mexico, whose growth can have a disproportionate knock-on impact on the rest of the world.
At the same time, tax havens that continue to refuse to disclose details of secret accounts will be named and shamed – as will countries that adopt a protectionist stance and block imports.
Tougher regulation of banks and restrictions on bank executives' pay will be introduced to prevent "rewards for failure".
Mr Brown, who spent weeks flying around the globe to lay the groundwork for the one-day summit in London, emerged after chairing the negotiations with a deal that committed the G20 to take "whatever action is necessary" to restore growth.
He contrasted the present crisis with the Wall Street crash of the 1930s, which took 15 years to fix. "This time, I think people will agree it's different," he said.
"We will not hesitate, as long as people are losing their jobs and their homes, to make the difference we can by improving their prosperity. Today's actions will not immediately solve the crisis, but we have begun the process by which it will be solved."
He described the package as an "international injection of resources", alongside measures to reform the financial systems that would create a "new world order".
The deal had been achieved by agreement between countries that, only a few years ago, would never have agreed to get round the same table, Mr Brown said.
French president Nicolas Sarkozy, who had threatened to walk out if the G20 failed to agree tougher financial regulations, said the deal "goes beyond what we could have imagined".
Describing Mr Brown as a "joy to work with", the French president said: "All of us are aware that we cannot go it alone. We need to reform the system, and I am truly delighted with this result.
"It was moving seeing countries as different as China and the US agreeing measures as precise as these."
Chancellor Angela Merkel, of Germany, who had previously sided with Mr Sarkozy against Britain and the US, said the deal was "a very, very good, almost historic compromise".
Mr Obama said he wanted to "underscore his appreciation" of Mr Brown's efforts, adding: "We have agreed on a series of unprecedented steps to restore growth and prevent a crisis like this from happening again."
Mr Brown denied the G20 had failed because it had not agreed a new fiscal stimulus.
"The issues that people thought divided us, did not divide us at all," he said.
"There was a substantial amount of agreement on the need for us to do whatever is necessary to return to growth."
But George Osborne, the shadow chancellor, said: "The great thing missing from this communiqu is the one thing the Prime Minister lobbied hardest for – that is, a new commitment to a significant second fiscal stimulus so that the Chancellor would have cover to announce one in the Budget later this month."
The final communiqu committed the G20 "to deliver the scale of sustained fiscal effort necessary to restore growth".
It set out six key pledges:
• To bring the shadow banking system, including hedge funds, within a global regulatory net, and to end tax havens.
• To clean up the banks and ensure that they begin lending more to families and businesses.
• To "do what it takes" to restore global growth and hasten economic recovery.
• To make international institutions strengthen their surveillance of the world economy.
• To act decisively to kick-start international trade after the collapse of last year's Doha talks.
• To help the world's poorest and commit to a "green" economic recovery.
The $1.1 trillion is made up of $500 billion in extra cash for the IMF – with $100 billion from the European Union, $100 billion from Japan and $40 billion from China – and $250 billion of "special borrowing rights", the IMF's version of "quantitative easing". The remainder of the package includes $250 billion of trade credits for developing nations and a $100 billion kitty to meet poverty and health targets.
Mr Brown said the deal took Britain "one step further" in being able to regain confidence in their banks. This, in turn, would boost jobs, he said.
Gold reserves held by the IMF will be sold, with the proceeds being spent on poor nations.
Nick Clegg, the Liberal Democrat leader, said: "Gordon Brown has clearly passed the test as a host to the world. He must now prove he can turn this deal into real help for British people."
NEXT STOP: JAPAN OR AMERICA
LONDON'S G20 summit was just the "beginning" of the long road to recovery.
World leaders will meet in the autumn in Japan or New York for another round of talks. Before then, in July, leaders of the eight biggest economies will gather in Sardinia, Italy, to guage progress.
Gordon Brown, the Prime Minister, has said hosting one G20 summit is enough for him.
While Silvio Berlusconi, the Italian prime minister, announced that Japan was ready to host the autumn summit, Nicolas Sarkozy, the French president, declared that it would be in New York, when world leaders are gathered for the United Nations' General Assembly.
Ministers deny any plans to tap into new IMF funds
MINISTERS last night were playing down speculation that Britain may have to seek a bail-out from the IMF.
Asked whether the UK would need to take advantage of the institution's newly expanded funds, Prime Minister Gordon Brown insisted he was "not proposing to do so".
"Countries have offered that they will take up the IMF facility – I think Mexico has yesterday – but we are not proposing to do so," Mr Brown told the G20 summit's closing press conference. But both Business Secretary Lord Mandelson and Treasury minister Stephen Timms raised eyebrows by stressing that the "stigma" had been taken out of using the IMF facility.
Pressed repeatedly over whether the UK might access the funding, Lord Mandelson said: "I don't think we are going to be first in the queue."
He finally added: "I don't think we are going to be in the queue."
The Conservatives have warned spiralling state debt may force the government to approach the IMF for a bail-out, as Labour did in the 1970s.
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