Arup, Bechtel, logistics expert DHL, Mott MacDonald and URS are drawing up the business case and delivery model for the 11-mile long electricity generating project.

Hafren Power, the consortium behind the ambitious plan, brought the consultants on board to deliver the plan to manage the consent and environmental approval processes and nine-year build strategy.

The proposed barrage between Brean in England and Lavernock Point in Wales would be the biggest single infrastructure project since the Channel Tunnel.

If built it would generate on the ebb and flood of the second largest tidal range in the world at 14m – an energy source capable of meeting some 5% of the UK’s annual electricity needs.

Tony Pryor, chief executive, Hafren Power, said: “Government has an open mind on our proposal and we are working hard to provide further details of construction, environmental and business impacts and mitigation.

“These companies have successful track records in delivering large infrastructure projects and are bringing considerable expertise and momentum to the process.”

He added: “As part of the energy mix, tidal power is greatly under-utilised. As a sustainable energy source the Severn estuary barrage will help the UK meet its renewable energy requirements. The engineering could also become the standard for schemes elsewhere in the world.”

The barrage’s 1,026 turbines would generate 6.5GW, making it one of the biggest power stations in the world.

Backers claim it would have a minimum lifespan of 120 years – far longer than any coal, gas or nuclear power station – and will probably operate for much longer than this.

On this argument Hafren power said its whole-life cost is lower than any known renewable or fossil fuel source.

Government approval is needed for the proposal, together with an agreement to support the electricity price in the first 30 years.