Leading article: Swim with the tide, Prime Minister

After any number of feasibility studies, over the course of nearly a century, plans to generate electricity from the vast tidal range of the Severn Estuary are again back on the agenda. And so they should be.

The case in favour of the Severn Barrage, always persuasive, is now more compelling than ever. Britain not only needs more green electricity and improved energy security, our ailing economy also needs a shot in the arm from large-scale building schemes. An 11-mile dam from Brean in England to Lavernock Point in Wales could produce up to 5 per cent of the UK's power without emitting any carbon. It would also create 20,000 jobs in its construction and support another 30,000 over the long term.

The good news is that the latest plan has a real chance. Where it differs from its immediate predecessor – rejected in 2010 – is that it does not require public money, at least not directly.Instead, the £30bn investment is to come from the private sector, a significant slug of it from sovereign wealth funds. Some help is still required from the Government, namely support for legislation authorising the scheme and a guarantee that long-term power prices will not slip too low – but no upfront cash.

With the trickiest financial hurdle potentially cleared, the Prime Minister is taking a renewed interest. Quite right. True, there are lingering environmental issues. Even with the use of more "fish-friendly" turbine blades, there are concerns about the impact on the Estuary's aquatic life and birds, too, may suffer, not least from any erosion of nearby mudflats. But green groups acknowledge that much has been done to mitigate the impact on local wildlife and any remaining issues cannot be allowed to be insurmountable.

With the economy in the doldrums, any number of Keynesian infrastructure schemes have been put forward. David Cameron has so far preferred an easy life – dodging the issue of airport capacity in the South-east, for example. He should back the Severn Barrage project and he should do it quickly, not least while the memory of the Olympics – on time and on budget – is still fresh.