The switch to windpower could see £6 billion a year added to the nation’s power bills by 2020 - equivalent to around £250 per household, the government’s own figures have revealed.

The money would be used to support a system of lucrative subsidies to the power companies that build and operate wind turbines.

It would also support the installation of 7,000 new wind turbines. At current prices it means each turbine could generate more profit from subsidy than from the sale of the power generated.

The costs would be in addition to the extra charges already arising from surging fossil fuel prices.

Last month alone saw millions of householders hit by £200 a year energy bill increases after EDF put gas tariffs up by 22 per cent and power by 17 per cent.

Other energy companies are expected to follow and some analysts predict total rises of up to 40 per cent by Christmas.

It means that, since 2003, the average annual domestic power bill has risen by more than 50 per cent to nearly £400 while gas has risen from £300 to £630.

The figures for the extra cost of green power emerged from Dberr, the business and energy ministry whose recent renewable energy strategy trumpeted plans to build 3,000 5-megawatt wind turbines in the seas around Britain with another 4,000 in windy areas onshore.

Less clear, however, was the potential cost of those machines but now a series of unpublicised technical reports from Dberr have shown how hard the switch to green power might hit the nation’s wallets.

One shows how the new turbines would generate around 86m megawatt hours of power each year. This would enable wind farmers to claim around 113m so-called Renewable Obligation Certificates, - the name given to the government subsidy system designed to promote green power generation.

Under this system wind farmers can claim one Roc for every megawatt hour generated by an onshore windfarm and 1.5 Rocs for the same amound of power generated offshore.

Rocs are currently worth £53 each so this translates into a total cost of just over £6 billion - all of which would be added to the bills issued to Britain’s 25m domestic consumers and 2m businesses.

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