Scotland has come top of a league table of the UK's most polluting power stations.
Campaigners Friends of the Earth Scotland claim that two coal-fired stations located north of the border are among the most inefficient in the country.
Cockenzie power station is located in East Lothian
But the allegations have been refuted by ScottishPower, which runs the facilities at Cockenzie in East Lothian and Longannet in Fife.
Friends of the Earth published the league table to mark the launch of its Carbon Dinosaurs campaign.
The environmental group said coal-fired stations pump out three times as much greenhouse gases as new gas-fired stations.
The campaigners are concerned about global warming and say the carbon dinosaurs have no place in a modern, clean energy system.
POLLUTION LEAGUE TABLE
Cockenzie, East Lothian
Ferrybridge, West Yorkshire
Fiddler's Ferry, Warrington
Kilroot, Northern Ireland
West Burton, Nottinghamshire
Eggborough, North Humberside
Aberthaw, South Glamorgan
Drax, North Yorkshire
ScottishPower's Cockenzie plant tops the league table of inefficiency, which was compiled from data provided on the UK's 16 coal-fired stations.
The pressure group said it produced the highest level of carbon dioxide per unit of electricity last year.
The 36-year-old plant in East Lothian is nearing the end of its life.
Longannet, which is located next to Kincardine, is placed third on the list - with a similar "fossil factor" to Ferrybridge in West Yorkshire, which is in second position.
Friends of the Earth Scotland chief executive Duncan McLaren said: "The latest figures show that, compared with the rest of the UK, Scotland is falling behind in cutting its carbon emissions.
"One of the main reasons for this is the presence in Scotland of two of the UK's top three most polluting coal-fired power plants.
"The government must ensure Scottish Power's plants clean up their act and make major cuts in its carbon emissions.
"Unless Scotland's carbon dinosaurs adapt, they will rapidly face extinction."
However, the claims were questioned by ScottishPower, which said the figures were incomplete and simplistic.
"Just as a car in the stop-and-start of city traffic uses more petrol than the same car on the motorway, these plants may appear less efficient because they are turned on and off to match periods of high demand," said a spokesman.
He added that the company was a major developer of wind power, and was also investigating the burning of other less polluting fuels.
A spokesman for the Scottish Environment Protection Agency (Sepa) said power stations were regulated under pollution control legislation.
"We set conditions and limits for emissions for individual sites and take appropriate enforcement action if authorisations are breached," he said.
A spokeswoman for the Department of Trade and Industry said the government was committed to cutting carbon emissions by 60% by 2015.
"Most recent figures show we are well on the way to achieving this," she said.
"The government is working with the industry, the regulators and various environmental groups to achieve this."