State-controlled banks such as Royal Bank of Scotland and Lloyds Banking Group should be forced to invest in renewable energy schemes, helping to kickstart a transition to a lower-carbon economy, Lord Browne of Madingley writes today.

In an exclusive interview with The Times, the managing partner of Riverstone Holdings, the private equity firm, and former chief executive of BP says that the Government’s commitment to build 25 gigawatts of offshore wind generating capacity by 2020 — equivalent to a fortyfold increase from present levels — is an “ambitious but achievable” target.

“The biggest obstacle is lack of credit,” he says. “This could be alleviated by directing state-controlled banks to lend more to projects in the supply chain and by working with the European Investment Bank to speed up implementation of its programme of green lending.”

Britain has 2,537 operational wind turbines capable of generating 3.6 gigawatts of electricity. However, plans to build new wind energy schemes have been hit by restricted access to finance over the past 18 months. Weaker oil prices have also undermined the economics of the industry.

A string of companies have cut their investments in the sector, including Shell and BP, which Lord Browne left in 2007. Iberdrola Renovables, of Spain, the world’s largest wind farm developer, has said that it will cut its investment programme in renewable energy from €3.8 billion in 2008 to €2 billion (£1.7 billion) in 2009.

Lord Browne believes that Britain has natural advantages in the field of offshore renewable energy: “As a crowded island with a complex relationship with its land, the obvious place to excel is in offshore wind and marine renewables, building on the marine engineering expertise found within the North Sea oil and gas industry.”

He says that it is important for politicians to be honest with consumers about the cost implications of the Government’s push to generate 35 per cent of Britain’s electricity from renewable sources by 2020. “The costs of deploying more low-carbon energy will be borne by consumers through higher household energy bills.”

However, Lord Browne says that the costs could be lower than some have claimed and may be limited to as little as a few percentage points over the next 20 years. This would be “significantly less than the double-digit increases in average gas and electricity bills caused by the spike in fossil fuel prices during 2007-08”. Lord Browne argues that energy efficiency is a win-win deal. “As well as reducing emissions, the net present value of most energy efficiency investments in our homes, offices and cars is positive.”

Ernst & Young estimates that it will cost more than £100 billion to build enough wind turbines to supply 20 per cent of Britain’s electricity.

Lord Browne says that establishing a price for carbon would be essential to achieving these aims.

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