Thousands of campaigners across the UK are taking part in a marathon lobby of MPs and a series of protests this weekend to call for a shake-up of global trade rules.
Delia Smith has joined the campaign for fairer trading
The mass demonstration Scale Up for Justice is calling on the government to put pressure on the World Trade Organisation to rewrite its laws in favour of poor countries.
The Trade Justice Movement, a coalition of 40 groups, is attempting to lobby all 659 MPs in their constituencies during the 24-hour protest which started on Saturday.
Julian Filichowski, director of the Catholic aid agency, Cafod, told the BBC the current system was grossly unfair.
He said: "The world trade system works against the poor of this world.
"We believe the system has to be radically altered to favour the poor.
"One billion people live on less than a dollar or 60p a day. That is a scandal."
He said Third World producers could not compete against subsidised agriculture.
"It's like a football match against Manchester United and the local parish team. You can have rules and a referee but it's not a fair game," he said.
The event has been arranged ahead of a World Trade Organisation meeting in Cancun, Mexico, in September.
Across the country, campaigners are meeting MPs or are gathering in city and town centres.
Celebrity chef Delia Smith was among those taking part.
Protesters from south London were meeting Streatham MP Keith Hill.
"Trade rules have the potential to reduce poverty and protect the Earth's natural resources," said Brixton campaigner Chris Holt.
Elsewhere in south London, MPs were being lobbied in Vauxhall, Balham, Battersea, Stockwell, Bromley, Croydon, Lewisham, Dulwich and West Norwood.
In the North West, protestors were gathering at the Pier Head, Liverpool, and St Ann's Square in Manchester city centre.
Hundreds of "trade justice" balloons were to be released.
In Birmingham, protest organisers said they expected hundreds of people in Victoria Square to call for a better deal for poorer countries.
Suffolk MP David Ruffley, who represents Bury St Edmunds, is hosting an event at St John's Church in the town.
He said: "They (developing nations) want the right to sell the textiles they make in their countries to sell it on fair terms to the European Union.
"At the moment the EU is stopping them from doing that."