Future coal-fired power stations could provide a cleaner, more environment-friendly alternative to renewable sources such as wind farms, according to a think-tank report.

The Centre for Policy Studies argues new, clean technologies can greatly reduce the environmental impact of coal-fired generation.

But the report, Clean Coal - a clean, secure and affordable alternative, points out that countries that rely on wind energy often have to bring back into commission older, "dirtier" stations to cover regular gaps in supply.

Dr Richard Dixon of the pressure group WWF Scotland, which recently named ScottishPower's Longannet power station in Fife as the 15th most polluting station in Europe, called the report "bonkers".

He added: "It is perhaps ironic that Thatcher's think-tank is now promoting coal after she ensured most of it would come from overseas."

The report claims: "An over-zealous policy in support of renewables can be counter-productive. Indeed, it can lead to a rise in carbon emissions, as older, less-efficient stations have to be brought back on-stream to plug the gap left by underperforming renewable resources."

Friends of the Earth also rejected the findings, saying: "There is no such thing as clean coal - only less dirty coal which can be achieved by more efficient generation"