The spectre of 1933 hangs over this week’s G20 summit. Then, as now, the world economy was reeling from a huge financial shock and trade was collapsing. When 66 countries attended the 1933 London Monetary and Economic Conference, Europe and America were divided and Franklin D Roosevelt did not even turn up. The conference flopped and the next attempt at international co-operation was not until after the depression gave way to war.

When Barack Obama makes his first big overseas trip as president for this London summit, there are echoes of the old disagreements. Angela Merkel has introduced a significant fiscal stimulus in her own country. But the German chancellor has emerged as the voice of European fiscal conservatism, unprepared to cede further ground, despite being urged to do so by the new US president.

Mr Obama, whose first two months in the White House have been bumpy, needs a successful summit. Brazil’s president has blamed the crisis on “white, blue-eyed” bankers and many US voters feel the same. They fear the latest $1 trillion bailout will benefit the same Wall Street bankers who brought the world economy down. They also think the Obama administration’s $800 billion stimulus package means America is carrying the weight of the world on its shoulders.

The president at least has time on his hands. Gordon Brown does not. Since November, when the prime minister started building up this conference as a means of saving the world, he has raised expectations far above what could reasonably be delivered. Long experience of international meetings should have taught him that most end in disappointment and a bland communiqué. But Mr Brown has been on a mission, zigzagging the globe in search of allies. Last week brought his hopes of delivering a big package of tax cuts and spending to a halt. The Treasury had been trying to steer him away from it for weeks but it took Mervyn King’s public comments and a failed auction of government bonds for the penny to drop. To be attacked by the owlish Bank of England governor recalls Denis Healey’s “savaged by a dead sheep” jibe at Sir Geoffrey Howe, but Mr King was both effective and right.

The public finances are too bad for any giveaway, thanks to Mr Brown’s profligacy and the recession’s devastating effect on tax revenues. That is why Britain’s contribution to what Downing Street says is a $2 trillion worldwide fiscal stimulus has been modest. If there is a “global new deal”, it will not be countries agreeing to throw lots more cash at their economies. That said, the G20 need not be a waste of time. “Do no harm” is not a bad motto and the leaders could achieve three important objectives. The first is to stand up forcibly against protectionism and in favour of free trade. The second is to give the International Monetary Fund far more cash for global fire-fighting. Finally the summit should speed up the process of closing regulatory gaps that allowed this crisis to develop.

The G20 will be accompanied by street protests that police warn will be “very violent”. Sometimes such protests change things, as in Seattle in 1999 when the World Trade Organisation was forced to switch its emphasis to the needs of the developing world. This week’s protests will tell us that people feel impotent in the face of global markets and that they hate bankers for precipitating the crisis. The risk is that the summit is remembered for violence outside and disagreement inside. The world economy is chaotic enough. This week should not add to it. That really would recall 1933.