The Liberal Democrats have overwhelmingly rejected calls for a Severn Barrage to be built, fearing the costs of the £20 billion power generator far outweighed the benefits.
Northavon MP Steve Webb, who has led the party's investigation into harnessing power from the estuary, told delegates at the party's annual conference in Bournemouth that the environmental impact, cost and timescale of the Weston to Cardiff scheme – which would provide more than eight per cent of the UK's electricity – were too great.
As well as "trashing" the Port of Bristol, it would decimate wildlife and take 20 years to build.
Instead he called for them to back the much smaller scale 'shoots barrage', which would be located downstream of the new Severn road bridge and would cost around £2.3 billion to build. It would only generate around an eighth of the power of the larger development.
Mr Webb told conference: "We looked at the big barrage, the Cardiff to Weston barrage, and we rejected it on several grounds. The government doesn't think it would generate power until 2030, and we need renewable electricity preferably yesterday. We can't wait 20 years. We would get 80 per cent loss of inter-tidal habitat, you can't compensate for that."
Bristol Councillor Mark Wright told the conference he would like the Weston to Cardiff barrage to be given the go-ahead, but feared it would be tied up in a legal quagmire for many years.
Bristol delegate Mary Page called for all barrage plans to be dropped, telling the conference that even the small version would devastate wildlife.
She said: "We are just caretakers, not the overlords or undertakers of the barrage."
A Government consultation is under way, with five options up for consideration on the Severn, including the two versions of a barrage. It is expected to report back early next year.