Britain is to sign up to a legally-binding pledge to cut its greenhouse gas emissions by 80 per cent by 2050.
The move, announced today by the new Energy and Climate Change Secretary Ed Miliband, makes the UK the first country in the world to commit to such swingeing cuts in the production of carbon dioxide and other gases blamed for global warming.
It comes after the Government-appointed climate change committee chaired by Lord Turner last week recommended that the UK raise its target from 60 per cent to 80 per cent cuts in emissions compared to 1990 levels, covering all sectors of the economy, including shipping and aviation.
In his first statement to the House of Commons in his new role, Mr Miliband told MPs: "The Government accepts all of the recommendations of the Committee on Climate Change.
"We will amend the Climate Change Bill to cut greenhouse gas emissions by 80 per cent by 2050, and that target will be binding in law."
Mr Miliband also announced that the Government was ready to legislate to force energy companies to introduce fairer pricing for customers with pre-payment meters if they would not do so voluntarily.
Energy regulator Ofgem has warned that many households with pre-payment meters are being "overcharged", he told MPs. And the regulator has also highlighted "unjustified" higher charges being paid by four million electricity customers in areas which are not linked up to the gas mains.
Mr Miliband said: "Unfair pricing which hits the most vulnerable hardest is completely unacceptable.
"I made that clear to the representatives of the big six energy companies when I met them yesterday.
"I also told them that the Government expects rapid action or explanation to remedy any abuses and I will meet them again in a month to hear what they have done ...
"If the companies don't act in a satisfactory way, then we will consult on legislation to prevent unfair pricing differentials ... There is more to do to protect consumers, and we will not hesitate to act."
Mr Miliband also signalled new help to encourage small-scale electricity generation though technology such as home-based solar panels and wind turbines.
He told the Commons the Energy Bill would be amended to introduce a "feed-in tariff" to guarantee prices for micro-generation projects which are able to supply electricity to the national grid.
Lord Turner last week said the UK's 60 per cent target needed to be tightened because new information suggested climate change was happening more quickly and the dangers were greater than previously thought.
In a letter to Mr Miliband, Lord Turner said the tougher target would be "challenging but feasible", and could be achieved at a cost of 1 per cent to 2 per cent of GDP in 2050.
He also said a cut of 80 per cent on 1990 levels by 2050 should cover all the major greenhouse gases - not just carbon dioxide - and all sectors of the UK economy, including shipping and aviation.
But because of practical problems in allocating emissions of international transport to the UK, they should not be included in the Climate Change Bill's five yearly carbon budgets, he said.
Instead the overall target should be "at least 80 per cent", with greater reductions in sectors covered by the Bill if aviation and shipping did not make sufficient cuts by mid century, he said.
Mr Miliband today acknowledged independent research suggested the threat of climate change was greater than previously thought.
"Arctic sea ice has melted faster than expected," he said. "Global emissions have grown faster. And the impacts of each degree of climate change are known to be worse."
On a day when cracks were appearing in the EU's plan to cut carbon emissions, Mr Miliband insisted commitments to reductions must come not only from Britain but from Europe too.
"That means an agreement by the end of this year on the strengthening of the EU Emissions Trading Scheme and on the targets for 2020: that Europe should reduce greenhouse gases by 20 per cent unilaterally, 30 per cent as part of a global deal; and that the EU should confirm its renewable energy target," he said.
Today's EU summit in Brussels has seen calls from Italy and Poland for the tough environmental targets to be dropped in the light of the current economic crisis.
Italy's Prime Minister, Silvio Berlusconi, warned the targets were now unattainable because of the financial burden of crashing markets and imminent recession.
And Poland expressed deep reluctance to meet pledges all EU governments made last year to cut CO2 emissions by 20% by 2020.