Peter Hain has backed plans to build a huge energy-generating barrage across the River Severn.

A new report suggests that harnessing the estuary's tidal flows could produce five per cent of the UK's electricity.

And the Wales secretary said Gordon Brown was "excited" about the proposed barrage, and that while the cabinet had been initially sceptical when the idea was first raised, there is now "real enthusiasm".

"It compares on a scale with the Channel tunnel, apart from this is above ground for everyone to see," he said.

The barrage would be important for Wales, South East England and Britain as a whole, as well as for the environment, he said.

"If we're serious about the fight against climate change, and if we're serious about clean, green energy, then this is the best example of it," Hain argued.

Environmental groups have criticised the plans, but Hain insisted he is an environmentalist and warned that there were no viable alternatives.

"I'm as green as they come as a minister, and this is about protecting the environment," he added.

On the economic benefits, he said: "It would be a huge generator of jobs, in the most spectacular construction project anywhere in the UK, and one of the biggest in the world.

"It will offer the prospect of rail and maybe road links from the south west of England to south Wales. It could even carry a potential channel tunnel rail link.

"Cardiff Airport is just around the corner from where the barrage would be, and there is big potential for it to become truly international."

Hain welcomed the report and said he wanted to see work start on the barrage as soon as possible.

He said: "Climate change is the greatest challenge facing this country and the global community and, if Britain is to play a leading role in meeting this challenge, projects such as the barrage cannot remain ambition forever."