In the east of England the skies seem unnaturally wide. Lift your eyes from the fields of gently waving wheat and barley and there is nothing to interrupt the broad skyscape. But not in Drax. Here the largest coal-fired power station in Europe rises from the floodplains like a great beast, belching steam and gas into the air in an unending stream.

It is as a terrible beast that the plant is seen by the 600 climate change activists who have for the past week been living in a squatters' camp near by. Drax the Destroyer they call it, after a comic-book villain whose humanoid body was fashioned from the earth's soil and empowered with a malign human spirit.

Today, they say, they hope to bring Drax's destruction to a halt. Drax, which lies just to the south of the Yorkshire town of Selby, last year burned 9 million tonnes of coal. It emitted 20.8 million tonnes of carbon dioxide, making it the largest single polluter in the UK. It produces almost 4 per cent of the nation's CO2, as much as a quarter of all the nation's cars put together. Which is why it has been targeted in a "mass day of action" aimed at shutting the plant down today.

The authorities, determined to stop them, have flooded the area with more police than this part of the world has seen since the epoch-changing miners' strike of 1984-85. What is happening today marks a turning point too. For it is the first large-scale direct action protest aimed at combating climate change. It could become the template for things to come. For the past six days the 600 activists at the camp set up on farmland near the Barlow Common nature reserve have been undergoing disobedience training focusing on what they call "tools and tactics for blockading".

Their plans are thought to include a mass invasion, trespassing into dangerous areas of the plant in an attempt to force the management to shut down the generators which supply seven million of the UK's homes. Police are responding seriously to the threat to the plant. It produces 7 per cent of the nation's electricity and a shutdown could lead to power cuts.

Workers at the plant are looking on somewhat bemused. Drax, they say, is the cleanest and most efficient coal-fired power station in the UK, emitting less CO2 per unit of electricity produced than other coal stations. Why are the less efficient generators not the target, they wonder?

"We are just as committed to action on climate change, but working from the inside," says Melanie Wedgbury of Drax. She has plausible responses to many of the protesters' points on Drax's legal challenge to badly-formulated current EU carbon emission levels, on how changes in government rules on Renewables Obligation Certificates have forced reductions in the co-burning of eco-friendly bio-mass fuels and on why dodgy gas and oil suppliers in Russia and the Middle East mean coal must stay part of the UK energy mix.

Drax, they say, is the cleanest and most efficient coal-fired power station in the UK, emitting less CO2 per unit of electricity produced than other coal stations. Why are the less efficient generators not the target, they wonder? "We are just as committed to action on climate change, but working from the inside," says Melanie Wedgbury of Drax. She has plausible responses to many of the protesters' points on Drax's legal challenge to badly-formulated current EU carbon emission levels, on how changes in government rules on Renewables Obligation Certificates have forced reductions in the co-burning of eco-friendly bio-mass fuels and on why dodgy gas and oil suppliers in Russia and the Middle East mean coal must stay part of the UK energy mix.