'It's a wild, exciting place'

Jeff Thomas, a retired miner but active birdspotter, gazes out at the Severn estuary. "This is the only great wilderness in this part of the country," he says. "It's a wild, exciting place. I love it and don't want to see it vanish."

The vastness of the estuary, as seen from the Newport wetlands reserve in south-east Wales, is a shock. You walk from the visitor centre, all cappuccino and carrot cake, through reed beds full of twittering warblers, cross a wobbly pontoon bridge and suddenly a huge view opens up. There is little sign of human activity, just the odd yacht and the occasional sand dredger.

This landscape is all about nature: precious salt marshes, the vast mudflats, the two islands, Flat Holm and Steep Holm, the fast-moving water.

If the barrage, from Brean Down, in Somerset, to Lavernock Point, near Cardiff, comes about, the structure will look like a tiny black line from here. But Tim Stowe, director of the RSPB in Wales, believes the effect of that line will be immense. "One of the UK's most pristine, most important, sites will be destroyed." If the water flow is controlled, chunks of mudflats and marshes will be lost and many of the 65,000 birds using the estuary will go.

The Anglers' Conservation Association says stocks of fish such as salmon, sea trout and eels, which move through the estuary, will be "decimated" by the barrage's turbines. There would be knock-on effects further up the rivers Usk, Wye and Severn.

Aside from the energy produced, the barrage would create tens of thousands of jobs. The area might then see new waterside housing and parks. But it would ultimately mean the taming of the Severn estuary. And to fans of the wilderness that is a high price to pay.