A tidal reef scheme is potentially one of the best designs for extracting power from the UK's Severn Estuary according to a report commissioned by the Royal Society for the Protection of Birds (RSPB). The report, commissioned by the RSPB and written by engineering consultants Atkins, has been timed to coincide with the announcement by the UK government of a shortlist of proposals for tidal eneergy from the Severn due next month.

Professor Rod Rainey of Atkins said: "We believe this scheme could be more powerful but less costly than other plans being put forward, particularly the Cardiff to Weston barrage."

The tidal reef proposal has been submitted to the government by Evans Engineering, a company based in Cornwall that designs and builds innovative renewable energy systems.

The reef would stretch 12 miles from Minehead in Somerset to Aberthaw, in the Vale of Glamorgan.

It could open at set points to allow large container ships to pass and be built in sections, enabling the much earlier generation of power.

Rupert Evans, of Evans Engineering, said: "The potential of a tidal reef is enormous. As well as electricity, it could produce hydrogen for use in non-polluting cars or the gas network. Its construction would mean far less road traffic because of rail connections, and would require less material and cost significantly less than other tidal options or nuclear power.

"It would cut Britain’s carbon emissions by around 12 million tons annually, create more than 30,000 jobs during construction and give a global lead for local manufacturing companies, particularly in the marine engineering sector.

Dr Mark Avery, Director of Conservation at the RSPB, said: "The government must crack the problem of how to use the Severn’s tidal power without harming its wildlife.

"We already know a Cardiff-Weston barrage would cost far more than almost any other form of green energy and seriously damage sites protected by law.

"A tidal reef could reign in that damage, cost the taxpayer much less and be built more quickly. Ministers should look seriously at the enormous pitfalls of a conventional barrage and the potential for using the Severn’s tidal energy in a much better way."