Ministers were told to back fair trade in the biggest mass lobby of Parliament.
Campaigners from Brighton and Hove and Lewes met MPs Norman Baker, Ivor Caplin, David Lepper and Des Turner during Wednesday's lobby.
Activists from the World Development Movement, Oxfam, Christian Aid, Cafod and Friends of the Earth travelled to London for the demonstration.
They said trade rules were allowing rich countries to benefit at the expense of the developing world and said new agreements would make the situation worse.
Sarah Berger, of the World Development Movement, said: "All the Brighton and Hove MPs expressed sympathy for our cause so now we are going to make sure we keep them to their word.
"There have been so many broken promises from western governments, including our own.
"We are calling on our MPs to urge Tony Blair to take a stand for trade justice at the forthcoming world summit meetings."
The lobby was timed to coincide with up coming meetings of the EU heads of government and the G8 group of industrialised nations.
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