ScottishPower plans to develop a string of wind farms around the UK capable of generating 6,000 megawatts in a joint venture with Vattenfall, Sweden's state-owned power company.

The move will involve building up to 2,400 offshore wind turbines. In theory, that many turbines operating at full capacity could produce enough electricity to power four million homes, or 8 per cent of existing UK power-generating capacity, although offshore wind farms tend to operate at only 35 per cent of capacity.

The companies will bid together for a third round of licences to operate offshore projects around the UK that are being issued by the Crown Estate, which owns the nation's seabed.

“Great Britain is an important growth market for us and has excellent conditions for wind power,” Lars Josefsson, the president and chief executive of Vattenfall, said.

The Swedish company, Europe's fifth-largest utility, also said that it had bought the rights to develop Britain's biggest offshore wind farm, off the coast of Thanet, Kent. It said that the facility would have a capacity of 300MW and would cost about £780 million to complete, although it had paid only about £35 million to acquire the project rights from CRC Energy Jersey 1.

As well as wind-power projects, Vattenfall operates nuclear, coal and hydro stations in Sweden, Germany and Poland. Last year it had 4.7 million customers and a turnover of €15 billion (£12.2 billion).

Neither ScottishPower nor Vattenfall would estimate the cost of building 6,000MW of offshore generating capacity. Analysts said that it would be about £3million per megawatt, indicating a total of £18 billion.

Applications for the third round of tenders for offshore wind farms are due by early March.

Wind turbines are becoming more powerful, but present technology allows only 2.5MW of generating capacity per turbine, so 2,400 would be needed to produce 6,000MW of electricity.

Vattenfall's announcement was welcomed by the Government, which has ambitious plans for offshore wind energy. It wants to build 33,000MW of capacity by 2020, a figure that experts have said would be impossible without big changes to Britain's planning system and the National Grid. The credit crunch and the falling price of oil have also undermined the ability of many developers to finance wind projects.

The Government is smarting from the withdrawal of a number of key players from the industry in Britain, including Shell and BP.

Brendan Barber, the TUC general secretary, urged the Government to follow the call of Barack Obama, the US President-elect, for a green energy revolution that would create five million jobs.

Mr Barber said: “Our European competitors have already shown that there are jobs and money in green technology. Germany's renewable energy sector employs half a million people and has a turnover of €24 billion. In contrast, the UK employs just 7,000 in renewable energy, generating €360 million.”

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive