Malcolm Wicks, the energy minister, said Britain would source up to 15% of its power from renewables by 2020, but that did not mean it was backing away from the EU-wide target of 20% by the same date.

The targets were announced after the Guardian reported yesterday that ministers were planning to water down climate change pledges and were seeking lower renewables targets before binding commitments are framed in December.

Mr Wicks said yesterday that the Brussels deal did not specify that all EU members had to meet the 20% level, as long as it was achieved across Europe as a whole.

"We're negotiating with the European commission, but it's got to be a considerable figure," he told BBC's Newsnight. "It's got to be somewhere between 10% and 15%."

He also said Britain was contributing to the fight against climate change in other areas. "At the end of the day, renewables is a means to an end. The end is bringing down carbon emissions," he said. Leaked briefing documents prepared for Gordon Brown by John Hutton, the secretary of state for business, and obtained by the Guardian, revealed that the target Tony Blair had signed up to earlier this year (for 20% of all European energy to come from renewable sources by 2020) was expensive and came encumbered with "severe practical difficulties".

The documents also said Mr Hutton would tell Mr Brown that Britain should work with governments that were sceptical about climate change to persuade them to set lower renewable targets.

Mr Blair not only signed Britain up to the EU deal, but also made it an "aspiration" that Britain should achieve a mix of renewable energy sources equivalent to 20% of Britain's energy needs by 2020.

Yet wind power in the UK lags well behind Europe's frontrunners, while marine energy is still in its infancy.

The leaked report estimated that increasing wind, wave and solar energy from the current UK level of 2% to just 9% by 2020 would cost around £4bn.

Environmental campaigners have said they are concerned that the potential shift in government policy will mean Mr Brown will surrender any claim to international leadership on climate change.