In his first major speech on the environment since becoming Prime Minister, Mr Brown hinted strongly that he is ready to extend the Government's target of a 60% cut in Britain's greenhouse gas emissions by 2050, revealing that he has asked an independent committee of experts to look at the possibility of an 80% goal.

He announced talks with supermarkets and other retailers over the elimination of throw-away plastic carrier bags from British shops.

And he launched a new Green Homes initiative, with a website and phone hotline to advise householders how they can reduce the carbon footprint of their properties.

Environmentalists welcomed Mr Brown's confirmation that Britain is "absolutely committed" to meeting its share of an EU target to generate 20% of Europe's power from renewable sources by 2020.

The commitment could see a surge in energy from wind, waves, solar panels, waste and biomass, starting with an announcement expected soon from Business Secretary John Hutton for a "significant" expansion in offshore windfarms.

Speaking ahead of December's international climate change summit in Bali, Mr Brown published a statement setting out Britain's vision of a new global low-carbon economy to hold the rise in average temperatures to two degrees Celsius or less.

And he said that any agreement stemming from the Bali talks should include "binding emissions caps" for all developed countries after 2012 to ensure greenhouse gases peak within 10-15 years and are reduced by at least half by 2050.

The international community faces a "historic and world-changing" challenge to build a low-carbon economy over the coming 50 years, Mr Brown told the conservation charity WWF in a speech in central London.

But he said the task was both "technologically feasible and economically rational" and held out the promise of new environmental industries generating £1.5 trillion annually and employing 25 million people worldwide - one million of them in the UK.