Energy Secretary Ed Davey told a news conference in London it was a "historic" day.
He said the UK was facing a "looming energy crisis" in the next decade thanks to years of neglect and under-investment.
Much of coal and nuclear-generated energy will stop in the coming years.
"We have known for years this is coming, but no-one was willing to take tough decisions."
Mr Davey stressed the project included plans to cover the costs of de-commissioning, with the operators required to pay into a fund from day one.
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One story dominates Thursday's front pages with some newspapers printing emotive pleas to voters to keep the United Kingdom as one.
After a mild start temperatures should pick up, with the south of England seeing highs of 26C.
In Edinburgh tonight you can hear it and feel it. The buzz, the banter of the day and the thrilling sense something big is coming tomorrow.