The decision will allow the plant to continue operating beyond 2015 when it would otherwise have been forced to close.

ScottishPower chief executive, Philip Bowman, said: “We believe that installing FGD provides both a good investment opportunity and tangible environmental benefits. It will help us to maintain a balanced portfolio and will also contribute significantly to the security of energy supply in Scotland with the potential for Longannet’s life to be extended beyond 2020.”

The seawater-based FGD technology is to be installed by a consortium of Alstom and Amec at an estimated cost of £170 million ($292 million). Amec will be responsible for planning, site management, civil and structural design and construction management and its share of the project is valued at £91 million ($156 million).

Alstom will supply the seawater FGD pollution control system that will reduce sulphur dioxide emissions in line with the European Union’s Large Combustion Plant Directive. The contract is scheduled for completion in early 2009

The four 600 MW unit station, located at Kincardine-on-Forth some 30km west of Edinburgh, is the second largest in the UK and generates the equivalent of over 25% of Scottish annual electricity demand.