A search for new homes for more than 65,000 birds began yesterday as part of a study into building a Severn barrage.

John Hutton, the Business Secretary, announced a feasibility study into the barrage to establish whether the benefits would outweigh the costs.

He said that a barrage across the Severn Estuary would have the “breathtaking” potential to provide almost 5 per cent of Britain's electricity and reduce carbon dioxide emissions significantly. A barrage would operate like a hydroelectric dam to generate electricity, with the water being pushed in by the tide.

However, the £15 billion barrage would destroy large stretches of mud-flats, saltmarshes and other habitats vital to wetland birds that spend the winter in Britain. The estuary contains some of the most valuable bird habitats in Europe – attracting species such as Bewick’s swan, pintail duck, shelduck, curlew, dunlin and redshank – and there is a legal obligation to replace any such areas destroyed by developments.

The estuary is also important for fish such as lampreys, salmon, sea trout and eels, which could have their migratory routes along the Severn blocked. The two-year study will assess the cost of providing alternative areas of wetlands and the chances of finding suitable land.

More than 65,000 wetland birds are attracted each winter to sites that would be affected and they would need to be found alternative areas.

Saltmarshes are among the rarest types of habitat in Britain and to provide alternatives would almost certainly mean restoring them in other coastal regions. Similar work has taken place in parts of Essex but there remain doubts about how easy it would be for important fish species to transfer to restored areas.

Ornithologists have deep reservations about the Severn project and Mark Avery, of the Royal Society for the Protection of Birds, said that the Government needed “to think long and hard” before committing itself. “Supporting this scheme to the tune of £15 billion would not leave much spare change for alternative projects should it fail to deliver, so the Government has to be sure it is the right place to risk so much taxpayers’ money,” he said. The Severn has been identified as a suitable site for a barrage because it has the second-largest tidal range in the world – the difference between the highest and lowest tides is up to 42ft (14m).

The feasibility study would be followed by public consultations if it were felt that the project should go ahead. It will look at several options, including the biggest proposal for a barrage between Cardiff and Weston-super-Mare and will consider tidal lagoons.

The estuary is designated as a special protection area and is in the process, because of its importance to lampreys, of being designated a special area of conservation. It contains several Sites of Special Scientific Interest.

Times recommends

• Energy-saving ideas from switched-on professor
• Rooks are as clever with tools as chimpanzees
• Burping of the lambs blows roast off menu