A bid to build a power generating Severn barrage has suffered a knock-back after the Government said it failed to show sufficient benefits.
The criticism of the plans for a £25bn barrage spanning the Severn was welcomed by environmental groups who called for a renewed focus on less-environmentally damaging ways of harnessing the estuary's tides to generate power.
The 11-mile barrage proposed by Hafren Power could generate 5 per cent of the UK's electricity from a renewable source – the huge tidal range of the estuary.
But the plan has already come under fire from the Energy and Climate Change Committee, which warned the proposals did not make a strong economic case and raised serious environmental concerns over the damage it could do to the estuary.
In its response to the committee's report on the barrage plans, the Government said that "in its current form, the Hafren Power proposal for a Severn barrage does not demonstrate that it could deliver the benefits it claims it would achieve".
The Government backed the committee's finding that plans did not "credibly demonstrate" sufficient mitigation of environmental concerns or damage to the local economy such as activity in ports upstream of the proposed barrage.
"Nor does it demonstrate sufficiently good value for money for the consumers," the Government said.
It added that there were many ways to meet targets to cut carbon emissions and the focus was on technologies that could meet those goals, while protecting the environment and delivering economic benefits and value for money for consumers.
The Government said it would need much more information from Hafren before it could further consider the proposal seriously, including in-depth studies of environmental impacts and evidence to substantiate claims on the benefits.
The move was welcomed by conservation and angling groups, who have opposed a series of proposals for a Severn barrage over concerns it could damage the important habitats of the Severn estuary and the rivers that flow into it.
Kate Jennings, from the RSPB, said: "Once again, plans to build a Severn barrage have been effectively dismissed, described as 'hypothetical' and failing to demonstrate either effective mitigation of environmental impacts or value for money.
"This is fantastic news for the wildlife of the Severn, and a welcome blast of common sense from the Government.
She added: "It's disappointing that Government has failed to more explicitly rule-out any further consideration of damaging barrage technology, but let's hope this is the final nail in the coffin for this outdated and discredited technology which has held back the development of innovative, clean, green tidal power schemes.
"This barrage has been a diversion from the real task of finding innovative ways of generating clean electricity whilst safeguarding the precious wildlife of the estuary."
Friends of the Earth South West campaigner Mike Birkin said: "We should be doing far more to generate power from the tides and waves, but these plans have been hugely over-hyped and threaten wildlife and our environment.
"Ministers should get behind less damaging, smaller-scale power schemes in the Severn and help build a world class marine energy industry Britain can be proud of."
Developers are preparing to put forward proposals for a £650m tidal lagoon in the Severn Estuary, with a six-mile wall around Swansea Bay to harness the tides to produce enough renewable electricity to power 120,000 homes by 2018.