As a result, the alliance is concerned comparisons made between the different schemes were biased against those involving innovative technology, which could actually be less harmful to the estuary’s special wildlife, ecology and landscape.

Such schemes failed to make the shortlist and were instead left to compete for a small pot of £500,000 development funding.

The Atkins review also concludes the shortlist was drawn up too soon.

It recommends proper development funding be given to potentially less environmentally damaging schemes, which should be reconsidered against the other projects once more up-to-date and balanced calculations of power, cost and environmental impacts have been made.

Martin Harper, Head of Sustainable Development at the RSPB, said: “The Government doesn’t need to rush to judgement on this. If they do, there is a serious risk they will pick the wrong project.

“As this review shows, that could mean unnecessary damage to the environment, an oversized bill for the taxpayer and all for less electricity than is possible.

“We have a real opportunity to build something on the Severn which becomes the gold standard for environmentally friendly tidal power and a template for other schemes around the world.”

Brendan McCarthy, Regional Director for the National Trust in Wessex said: “The National Trust recognises the need to dramatically increase the amount of electricity we generate from renewable sources, and we support a full assessment of ways to harness the power of the Severn Estuary as part of this.

“However, we're concerned that the process has not given fair weight to the immense value of our natural and cultural environment. Nor do we think it has properly assessed the potential of more innovative technologies to provide a better solution than the well-known but expensive and damaging Cardiff-Weston option.

“We believe the Government needs to pay close attention to the report we have commissioned. We want the study to continue but in a way that will ensure the final project provides the UK with an important source of renewable electricity, whilst protecting the rich wildlife and striking landscape of the Severn, and making best use of public money.”

Martin Spray, WWT’s Chief Executive, said: “The need to reduce our greenhouse gas emissions is urgent, but there are ways of doing this that do not destroy our best wildlife sites.

“The current short list is biased against schemes that aim to reduce environmental impact but these innovative new technologies may be part of the solution. Government needs to increase the funding pot to speed up their development.”

Dr Stephen Marsh-Smith, Executive Director of the Wye & Usk Foundation and chairman of the Angling Trust, said: “Measures to combat climate change and generate electricity are urgent.

“The study has failed to address, early enough in the short listing process, the requirements of EU environmental legislation and the recommendations of the Sustainable Development Commission with the result that highly damaging schemes are included which could extinguish, runs of unique migratory fish such as salmon, lamprey, eels and shad. As a result there will be significant delays while more environmentally friendly schemes are (re)considered.”