Campaigners and MPs have called on Tony Blair to support moves to give the world's poorest countries a better deal from increased economic globalisation.

Thousands of people from across the UK gathered in Westminster on Wednesday to lobby their MPs as part of a campaign to get Western countries to scrap protectionist measures such as the Common Agricultural Policy.

A cross-section of people from church groups and trade unions to students and school children protested.

Many said that the G8 summit in Canada was an ideal opportunity for the prime minister to put his words into action.

Most said their involvement in the campaign had begun with the Jubilee 2000 lobby to end world debt.

Liz Holman, from Bassetlaw in Nottinghamshire had travelled to Westminster to lobby Labour MP John Mann.

"What this may do is give a voice to those from the poorest countries of the world who can't be here to make themselves heard. I am against exploitation," she said.

"Tony Blair and Gordon Brown should take a stand at the G8 summit meeting. I hope very much that we are not going to follow George Bush with the idea of farming subsidies."

Peter Persico, a student who had travelled from Leeds, urged the politicians who will be at the G8 summit to make an agreement - however limited in scope.

"Politicians often say 'we have to take this or that into consideration'. They can at least get something down that they can work from," he said.

There was backing for the campaign from a cross-section of MPs.

Labour MP Helen Clark gave her backing to the campaign, saying she would write to trade secretary Patricia Hewitt on the issue.

"I am particularly concerned that the European Union is pressing to include water services in the General Agreement on Trade and Services (GATS), talks on which are due next week," she said.

"Many countries in the developing world have already come under pressure from the World Bank and International Monetary Fund to privatise their water supplies and this has often raised prices above the level that poor families are able to afford, forcing them to collect water from untreated sources, such as rivers, which is of course a health threat."

South East Cornwall MP Colin Breed met with some of his constituents who had attended the rally. "We must stand up and fight the enormous disparity between the developed countries and the struggling countries. We are supposed to be a civilised country yet we allow unacceptable poverty to continue," he said.

"This is such an important issue that I was even lobbied today by my own wife! I hope that Tony Blair hears what is being said today and takes that message to the table of the international community."

Fellow Lib Dem member Dr Jenny Tonge, the party's spokesman on international development, said the campaign was about empowering communities.

"The lobby should be a huge success with thousands of constituents from all of the country lobbying their MPs at Parliament. I hope they will all listen to what the Trade Justice Lobby wants."