A giant offshore power cable taking green energy from Scotland to the south of England is "technologically and economically viable", according to a detailed report published today.

The undersea line along the east coast would revolutionise the Scottish renewable energy industry by transmitting wind, wave and tidal power from stations across Scotland to the rest of the UK and Europe.

The main transmission system would connect Shetland and Orkney to Peterhead and then south to Norfolk and on to London at a cost of £1.7bn. But the vision for a total network for 2020 with additional connections to the Western Isles, Dounreay, Torness and eventually to Europe, would cost around £4.8bn.

The ambitious project is detailed in a new study by the Crown Estate and comes as the Scottish Parliament prepares to hold a debate on energy.

Opponents of the controversial Beauly-Denny overland power line welcomed the undersea alternative, although the study stresses there would still need to be reinforcements carried out to the onshore transmission network.

Rob Hastings, director of the marine estate at the Crown Estate said: "This report confirms that an undersea cable down the east coast is technologically and economically viable and we have now commissioned more detailed studies.

"The prospect of taking green energy right down the east coast to heavily populated areas in the south, and potentially to the rest of Europe, is incredibly exciting: today's report brings that key infrastructural development one step closer."

Tavish Scott the MSP for Shetland said: "We need a cable to make renewables happen in the islands and this east coast route is certainly one of the possibilities. Keeping the Home Counties lights on, at the right price, is something Shetland is very interested in.

"So we will want to assess this proposal in conjunction with others being produced."

Although the idea of an east coast subsea cable to take that power south has has been around for some time, the new study is the most detailed yet and the first to confirm its technological and economic feasibility.

Jason Ormiston, chief executive of the industry forum Scottish Renewables, said: "There is still a lot of thinking to be done, not least about who would pay for such a network, and who would manage it.

"But this report gives a big boost to that thinking and helping us find a way to get that power to market."

Helen McDade, policy officer of the John Muir Trust, said it vindicated those opposed to the controversial Beauly to Denny power line, who had argued that sub-sea cables had not been adequately assessed.

"This begs the question, why do we need Beauly-Denny? It's 20th-century technology being imposed on the 21st-century.

"We're delighted to see the Crown Estate and others are researching cutting edge technology."

Massive wind farms are proposed for both Lewis and Shetland and the European Marine Energy Centre on the Orkney island of Eday is pioneering wave and tidal power development with £15m worth of public support.

A subsea transmission system would take this power to the insatiable energy markets of the south east of England and Europe.

But Sir Donald Miller, former chairman of both the South of Scotland Electricity Board and Scottish Power, is not so sure.

He told The Herald: "It is technically feasible, but the cost would be absolutely horrific.

"We are talking about bulk power to the consumers with costs of about £120 per megawatt hour compared to bulk power in the market or nuclear station is about £30 to £35.

"So economically it would be absolutely ludicrous."