Another massive advantage of a Severn Barrage could be a new road link between Somerset and Wales, bloody handy for cavers,
Aaaarghhh. If it gets built there won't be any point because there won't be many caves left. About 30 years ago, when a smaller version of the barrage was proposed, approximately 150 quarrying licenses for limestone were approved in the Mendips and Wales, based on interim development orders granted after the 2nd World War. I know this because I was heavily involved in the attempts to get them stopped and, although a victory appeared to have been achieved at the time, I don't think they've gone away. At the time the Severn barrage was recognised for what it has always been, and that's got very little to do with saving the Planet, more like lining the pockets of major civil engineering firms.
I don't find your arguments very convincing Mick but maybe I'm just being cynical.