The cost of securing an 80% cut is estimated to be 1 to 2% of GDP in 2050.

Miliband told MPs: "In tough economic times, some people will ask whether we should retreat from our climate change objectives. 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".

Miliband alsoagreed to the demands of a cross-party campaign to amend the energy bill to create feed-in tariffs allowing small-scale energy producers ( e.g. wind turbines or solar panels on domestic homes) to sell their surplus electricity to the national grid at a guaranteed price. Countries such as Germany have been far ahead of Britain in allowing feed-in tariffs, so creating a huge solar industry.

He also claimed that in tough economic times, green jobs could be created in "a transition economy" if the country committed itself to radical climate change targets.

Friends of the Earth executive director Andy Atkins said: "We are absolutely delighted that Ed Miliband has committed the UK to cutting its emissions by 80%by 2050 - this is what the science demands."