The plans would affect Longannet power station in Fife and the Cockenzie plant in East Lothian.

First Minister Alex Salmond visited Longannet on Thursday afternoon for his first official engagement.

Scottish Power said the scheme would cut carbon dioxide (CO2) emissions at the two stations by a fifth.

It said the scheme would be the biggest clean coal project in Europe.

Salmond met the chairman of Scottish Power, Ignacio Galan, to discuss the plans at the site.

The first minister said, “It is crucial, not only for Scotland but for the planet, that we achieve a low carbon economy.

“We must do this not just by exploiting our nation’s renewables potential but also by deploying expertise in clean coal and indeed hydrocarbon technology.

“If we can reduce carbon emissions, coal can play a vital role in giving Scotland the diversity of energy sources which is essential for security of energy supply.“

Scottish Power, now part of the Spanish-based Iberdrola utility group, said the blueprint would see giant new turbines and low-emission boilers installed at the power stations.

The new “supercritical“ turbines and boilers would burn coal at ultra-high temperatures and pressures.

A feasibility study for the scheme has now started and if it goes ahead it would effectively mean building the new turbines and boilers within the existing stations.

Construction could start in 2009 with operations beginning in 2012.

Galan said, “We are delighted that today’s announcement puts Scottish Power on track to deliver a revolutionary change in low carbon energy generation in Scotland.“

Scottish Power said it hoped that the remaining CO2 would eventually be buried in the old Longannet coal mine.

The two plants currently account for a quarter of Scotland’s electricity needs.

Scottish Power is hoping to receive some encouragement from Westminster.

It would like to see a change to the rules under which Scottish companies pay more than English firms to transmit power to the National Grid.

Campaigners WWF Scotland said that it would be better to invest the money in green energy.

However, the proposals were welcomed by Friends of the Earth Scotland, which previously branded the two coal-fired power stations as “carbon dinosaurs“.

PIN/BBC