Campaigners from around the world set off on the Cut the Carbon March yesterday from Northern Ireland.
The march is believed to be the UK's longest protest march, calling for action on climate change.
Around 50,000 people are expected to join the 1,000-mile trek at different points, gathering signatures for a petition calling on Prime Minister Gordon Brown to bring in a new law forcing companies to reveal their carbon dioxide emissions.
The goal is to gather support for changes to the new Climate Change Bill, which will enter Parliament for discussion six days after the end of the march in October.
Christian Aid is calling on the UK Government to ensure the new Climate Bill includes a target for UK CO2 emission cuts of at least 80 per cent on 1990 levels by 2050 "so we play our fair part in keeping global warming below 2˚C".
It also wants to see the introduction of mandatory reporting of CO2 emissions by companies trading in the UK.
Christian Aid has urged the UK to take the lead in calling for a UN agreement on tackling climate change by cutting rich countries' CO2 emissions by at least 80 per cent by 2050.
Paul Brannen, head of campaigns at Christian Aid said: "Poor people in the least developed countries are already dying as a result of floods, droughts and conflict over already scares resources, such as water, that are becoming scarcer as the planet heats up.
"They need our help to tackle climate change by reducing emissions, through individual action and by putting pressure on the UK government to pursue climate-friendly national and international policies."
The Cut the Carbon March is backed by celebrities including singers Lemar and Amy Macdonald and actors Leonardo Di Caprio and the rising star from the latest Harry Potter instalment, Katie Leung.
The march will conclude at the London Stock Exchange on 2 October 2007.
