A global protest against UK plans to build new coal power plants is being launched today by campaigners from more than 40 developing countries accusing the government of being a "climate criminal".

They have written an open letter to energy and climate change secretary Ed Miliband that follows repeated warnings from UK groups that the decisions to approve new coal power plants and the expansion of Heathrow airport would damage the nation's position in international negotiations when it tries to persuade other countries to cut global-warming emissions.

The 27 groups, including campaigners from India, Brazil, Indonesia, the Philippines and Uganda, say they are "alarmed" that the UK government is considering allowing new coal plants to be built, including one at Kingsnorth in Kent. They blame emissions from rich countries for causing global warming and the "increased floods, droughts, sea-levels and disease" that threaten the livelihoods of "hundreds of millions of people".

"Coal power is the most climate-polluting way to generate electricity," continues the letter. "New coal power stations in the UK will exacerbate the impacts of climate change on impoverished communities in the south[ern hemisphere] ... A decision to support new coal power stations will confirm the UK as a climate criminal in the international climate-change negotiations."

The groups oppose the current plans to build coal plants with no equipment for carbon capture and storage (CCS), and existing proposals for a "demonstration" of the technology are inadequate, said the World Development Movement, the UK-based poverty campaigning charity which coordinated the letter.

The letter also criticises proposals to offset the carbon dioxide from coal plants by investing in clean technology projects in the developing world through the UN's Clean Development Mechanism, which the groups say has "continuously had negative impacts on communities in the global south while failing to cut emissions".