All the UK’s tidal resources acting together could provide 10% of the country’s electricity, according to a report, ‘Tidal Power in the UK’, by the Sustainable Development Commission, a government funded think tank set up in 2006 to act as the UK government’s watchdog and adviser on sustainable development. Nearly half of that, 17TWh yearly, could come from a tidal barrage in the Severn Estuary, the second greatest tidal range resource in the world. Such a barrage would expect to be functional for over 120 years.

Developing the barrage would result in significant climate change and energy security benefits, but would also have a major impact on the local environment, with the loss of up to 75% of the existing intertidal habitat, which is internationally protected. There would be a number of impacts on local communities and the regional economy, and a high risk that unsustainable ancillary development would take place alongside any barrage project. The SDC has therefore laid down a series of tough conditions which a Severn barrage would have to meet in order to be considered sustainable. These are the main ones.

• A Severn barrage must be publicly led as a project and publicly owned as an asset to avoid short-termist decisions and ensure the long-term public interest

• Full compliance with European directives on habitats and birds and a long-term commitment to creating compensatory habitats on an unprecedented scale

• Further investigation of the ‘environmental opportunity’ that might exist for combining climate change mitigation with adaptation through a habitat creation package that actively responds to the impacts of climate change over the long term.

The report also highlight sthe SDC’s contention that the lower rate of interest available to a Government-led project would provide the only realistic way of financing a large-scale compensatory habitat package, as well as providing electricity to consumers at a competitive price.

But the Commission warns that the development of major tidal power resources should not be seen as a licence to ignore the need for dramatic reductions in our energy consumption, increased energy efficiency, and the wider decarbonisation of our energy supplies. “The Sustainable Development Commission is issuing a challenge to Government to embrace a new way of managing this major project,” said SDC chairman Jonathon Porritt.

Neath businessman Gareth Woodham has put forward a change of use application for the estuary to planners in Somerset to allow a 10-mile barrage to be built. Mr Woodham’s plan would see a barrage linking Lavernock Point in the Vale of Glamorgan with Bream Point in Somerset, creating a tidal lagoon behind it. A road and rail link is also proposed over the top of it, along with 12 man-made islands and four marinas.

Sedgemoor council in Somerset has referred the application to the UK government, and the leader of the South West Regional Assembly is taking a fact-finding mission to the La Rance tidal barrage near St Malo in Brittany. Mr Woodham told BBC Wales: “There are already a number of major construction companies that are interested. “With the energy prices as they are today, it has become economically very viable.”

Three environmental groups, WWF, the Royal Society for the Protection of Birds (RSPB) and Friends of the Earth Cymru, have voiced their opposition to the scheme, saying that it would cause irreversible damage to wildlife. There are, they say, other technologies which could be used in the Severn estuary with a much lower environmental impact.

The estuary is a special area for conservation and provides food for more than 63 000 migratory and wintering water birds, representing seven per cent of the UK’s total estuary resources for wildlife.

Morgan Parry from WWF Cymru said the barrage was not the answer, adding: “The environmental damage caused by constructing a 10-mile concrete energy dinosaur will cause irreversible damage to Wales and England’s most important estuaries.”