In its latest survey of the worst power station pollution in the European Union, WWF said the "dirty 30" in seven countries pumped out 393 million tonnes of carbon dioxide in 2006, or 10 per cent of all EU CO2 emissions.

Greece's Agios Dimitrios plant maintained its status as the worst since the last ranking 18 months ago.

It was followed closely by another Greek station, Kardia, six power stations in Germany, Poland's Turow and the As Ponte power plant in Spain.

"The facts are clear: the power sector needs to phase out dirty coal as soon as possible," said Stephan Singer, head of WWF's climate and energy unit.

The top 12 in the ranking are fuelled by lignite, a low grade "brown coal", and were mainly first commissioned in the 1960s and 1970s. However, Agios Dimitrios, first went into service in the mid 1980s, according to WWF.

The rest were largely coal-fired, although the British power stations at Kingsnorth (24th) and Eggborough (29th) also use heavy fuel oil or gas respectively.

Britain and Germany shared ten of the dirtiest plants each, followed by Poland with four plants.

More than half of the dirty 30 are run by four power generation companies: Germany's RWE, Swedish firm Vattenfall, French group EDF and Germany's EON.

"We cannot tolerate a power sector where the dirtier get richer," Singer said.

He called on the European Union to improve its emissions trading schemes to ensure that only those who clean up their power stations reap a financial benefit.

The WWF report for 2006 ranked plants across the then 25-nation EU according to their efficiency -- a calculation based on the number of grammes of carbon dioxide (CO2) emitted per Kilowatt hour of electricity generated.

CO2 is the main greenhouse gas that trap the sun's heat causing global warming.

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