The protesters chanted slogans like "G8, the world can't wait" and blew whistles and horns.

Police said the London rally was incident-free. In Rostock, near the site of next week's summit, clashes erupted at an anti-globalisation rally when protesters attacked German police.

"This rally is to tell (Prime Minister) Tony Blair to make the G8 live up to the promises they made two years ago on AIDS, poverty and climate at their Gleneagles summit," anti-poverty campaigner and musician Midge Ure told Reuters.

The G8 summit in the Baltic resort of Heiligendamm from June 6-8 is expected to make declarations on a range of issues from foreign exchange to trade and global warming.

The leaders of major developing nations China, India, Mexico, Brazil and South Africa will also attend.

The United States is leading a group of countries including Canada rejecting moves by G8 president Germany to get the summit to commit to firm targets and timetables on cutting climate-warming carbon emissions.

Organisers said 10,000 people took part in the London demonstration but an eye witness put the figure at around 2,000.

It was a long way short of the 200,000 who marched through Edinburgh in July 2005, the weekend before the Gleneagles summit, at the culmination of the Make Poverty History campaign urging leaders of the rich world to lift Africa's debt burden.

Ure, who co-wrote with Bob Geldof the Band Aid record that galvanised people to raise money to alleviate the famine in Ethiopia in 1985, was unperturbed at the difference in numbers.

"Edinburgh march was magical. But it was unique," he said. "Make Poverty History was a very focused and effective campaign and 2005 was also the 20th anniversary of Live Aid and Band Aid so people were sensitised.