In reply to EeeByGum:
> I agree with your sentiment but this is hardly a new idea and I would imagine that its dismissal is more political than practical.
There will always be a substantial political component to such a decision, but as outlined above in the wikipedia description of previous studies, apart from informed comments by people like Ring-Ouzel, there are very substantial practical problems. It may just not be as good a scheme as it first sounds like.
> The coalition is currently pretty weak, especially with the current lobbyist scandal starting to build momentum
There opponents are even weaker however, while lobbying seems like standard Westminster village froth.
> The Severn Barrage project has the potential to stir deep seated emotions on both sides of the debate and would certainly bog down any government that proposed the idea as viable.
Similar to HS2, most people are in favour and it sounds like a magic bullet, until the costs and details become more apparent. But any major infrastructure project in a country as crowded as the UK is going to arouse masses of passionate objection, that does not mean we can forever put them off.