The "Dirty Thirty", most of which are coal-fired, produce 393 million tonnes of carbon dioxide (CO2), together responsible for 10 per cent of the bloc's CO2 emissions, the report said.
CO2, mainly from burning fossil fuels, is widely considered to be stoking global warming.
EU's "dirtiest" power stations
The EU's top two dirtiest power stations, in terms of grammes of CO2 per kilowatt hour, are in Greece, according to the Swiss-based WWF.
Those power stations, Agios Dimitrios and Kardia, are both run by Public Power DEH, Greece's largest power utility
Germany's least efficient plant was Frimmersdorf, owned by RWE, the German power giant, while the UK's least efficient plant was Longannet, owned by Scottish Power.
In the 1990s, Britain shifted much of its power generation to natural gas from the North Sea, but as gas reserves dwindle, generators have returned to coal power.
Poland, which joined the EU in 2004, had five power stations on the list, with Turow, owned by BOT GiE, as the country's least efficient.
The EU hopes to achieve a target of up to 30 per cent reduction in CO2 emissions by 2020, with an EU emissions trading scheme aimed at encouraging investment in cleaner, more efficient plants.
At the same time, most of the EU's dirtiest coal power stations will have to be decommissioned over the next twenty years.
Earlier this year, Germany announced plans to build 40 new coal-fired power plants, although it says new technology will allow the plants to be more efficient.
The WWF advocates replacing coal-fired plants with less CO2-intense natural gas or CO2-free renewable energies plants.
Governments are under pressure to act
over inefficient plants [GALLO/GETTY]
Governments around the world are under pressure to act over inefficient and polluting industries after the UN climate panel this year blamed human activities for stoking global warming
The panel said failure to halt emissions could result in more incidents of famine in Africa, water shortages for billions around the world and rising ocean levels.
"We have a closing window of opportunity in terms of putting a post-2012 approach in place," the Reuters news agency quoted Yvo de Boer, head of the UN climate change secretariat, as saying on Thursday.
UN delegates began meetings in Bonn, Germany, on May 7 to discuss ways to curb climate change.
Officials in Bonn are seeking ways to widen and extend the UN's Kyoto Protocol on limiting greenhouse gases, to include those outside of the protocol, including the US, China and India.
Kyoto binds 35 industrial nations to cut greenhouse gases by 5 per cent below 1990 levels by 2008-12 but Kyoto backers only account for about a third of world greenhouse gas emissions.
But some diplomats say it will take two years to negotiate a successor to Kyoto, and then another two years for national governments to ratify an agreement.
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