According to the latest survey by environmental group WWF, the only country with dirtier power plants than Germany was Greece.

Germany had six coal-burning plants among the top-ten most polluting sites in the European Union, the WWF survey showed. And it was tied with Britain for having the largest number of dirty electricity plants overall. Each country contributed ten plants to the total.

Overall, the WWF said, the Dirty Thirty in seven countries pumped out nearly 400 million tons of carbon dioxide in 2006. That's 10 per cent of all EU CO2 emissions.

"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.

Blaming lignite

Within Germany, the dirtiest power station was the RWE-run Niederaußem brown-coal plant (number three on the overall ranking.) It, and several others on the German list, is in the industrial state of North-RhineWestphalia.

The top 12 power plants in the overall EU rankings are fuelled by lignite, a low grade "brown coal," and were mainly first commissioned in the 1960s and 1970s. However, the number one offending plant, Greece's 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.

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

Calls for EU help

"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 grams of carbon dioxide (CO2) emitted per Kilowatt hour of electricity generated.

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