The electricity generated by the barrage would be equivalent to eight large power stations.

"No other source of renewable energy has the scale, reliability, predictability or proven technology of tidal power from the Severn Estuary, nor make the same contribution to security and diversity of supply from a single project," said the report by engineers Sir Robert McAlpine Limited.

A 13-year study into an 8,640 megawatt barrage in the Severn Estuary was shelved after racking up a bill of 67 million pounds ($107.5 million).

The scheme, which could supply six percent of England and Wales' power needs, ran into opposition from environmental groups and local inhabitants.

The report, published on the Department of Trade and Industry's website, said the barrier would also help reduce flooding in the Severn basin which could increase as a result of global warming.

The project could cost between six to 8.4 billion pounds, 40 percent lower than estimates made in the late 1980s, reflecting a significant fall in the cost of capital in recent years.

Britain has a target to increase the amount of power from renewable sources to 10 percent by 2010, from around three percent at present, and has indicated this could increase in future.

The earliest date that the barrage could start generating electricity is around 2012 with full power by 2014.

"The barrage would certainly be an important option if more increases in renewable electricity generation are required post 2020," said the report.

Britain has a domestic policy goal of cutting carbon dioxide emissions by 20 percent by 2010, greater than its legally binding commitment under the Kyoto climate change protocol.

Britain has no large-scale tidal barrages. A commercial tidal power scheme has been operating at St Malo in France since 1965.

Three tidal projects are under development in Wales - at Swansea Bay, Fifoots Point and Rhyl, where tidal ranges are high and local government puts a strong priority on renewable power.