The protest came ahead of a United Nations climate change conference in Nairobi, Kenya.
Protesters urged Britain's government to help negotiate a deal to keep global warming to less than two degrees centigrade.
The march came days after the publication of a study by former World Bank chief economist Nicholas Stern, which warned that if nothing was done global warming could cost up to 20 per cent of the world economy.
Several thousand demonstrators gathered outside the US embassy in London, calling for the US to ratify the 1997 Kyoto Protocol that sets targets for reductions in carbon dioxide emissions.