Britain became the first country in the world to make a legally-binding commitment to cut its greenhouse gas emissions by 80% by the middle of the century, in a dramatic effort to counter global warming.
The pledge came as the European Union reaffirmed its target of slashing carbon dioxide emissions by 20% by 2020, despite complaints from Italy and Poland that the tough standards will be unaffordable during the current economic downturn.
New Energy and Climate Change Secretary Ed Miliband told MPs an amendment to the Government's Climate Change Bill will increase the UK's target for emissions cuts in all greenhouse gases by 2050 from 60% to 80%, compared to 1990 levels.
"In tough economic times, some people ask whether we should retreat from our climate change objectives," he said.
"In our view it would be quite wrong to row back and those who say we should, misunderstand the relationship between the economic and environmental tasks we face."
The announcement was hailed as a "great step forward" by environmental campaigners, who believe that industrialised countries must lead the way in reducing global emissions by at least 60% to stave off potentially catastrophic changes in weather patterns.
But there were warnings that the impact of the pledge will be blunted because there is no immediate provision to include the UK's share of emissions from international aviation and shipping.
And campaigners cautioned that Britain must hit its new target by changes in behaviour at home - such as scrapping plans for coal-fired power stations - and not by emissions trading with less developed states.
In his first statement to the House of Commons in his newly-created role, Mr Miliband also pledged to introduce feed-in tariffs to allow small-scale energy producers - such as homes with wind turbines or solar panels - to sell electricity at a guaranteed price.
And he issued a warning to energy companies to come up with plans to reduce charges for customers with pre-payment meters within a month or face legislation to force them to do so.
