Artist's impression of a double rotor tidal machine

They hope that they can start installing an 80-tonne steel pile into the seabed, about a mile offshore from Lynmouth.

They will then fit the turbine and rig onto the pile, with the aim of testing how successful larger turbines would be in commercial energy supply.

Storms during the winter have held back progress on the Seaflow turbine, which will be Britain's first underwater windmill.

'Incredibly exciting'

The single 11 metre-long rotor blade will be capable of producing 300 kilowatts of electricity and will be a test-bed for further tidal turbines.

It is hoped to convert the system to twin rotors by the end of next year.

Project developers Marine Current Turbines Ltd and Cornwall-based Seacore declined to comment until the turbine is in place.

But renewable energy expert Steven Ward of the national charity, the Centre for Sustainable Energy, said: "I think it's incredibly exciting.

"The UK has a considerable tidal stream resource and up to 2% and possibly more of our electricity demand could come from tidal stream.

"That would form a major part of the government's aspiration that 20% of our electricity supply should come from renewable resources by 2020."

The project is financed by the Department of Trade and Industry and the European Commission's energy programme.