Energy Secretary Ed Davey gave consent for a new nuclear power plant at Hinkley Point in Somerset.
Plans for a nuclear power station at Hinkley Point C in Somerset, will "lock a generation of consumers into higher energy bills", Greenpeace said.
Executive director John Sauven said: "It will distort energy policy by displacing newer, cleaner, cheaper technologies.
He added, "With companies now saying the price of offshore wind will drop so much it will be on par with nuclear by 2020, there is no rationale for allowing Hinkley C to proceed.
"Giving it the green light when there is no credible plan for dealing with the waste could also be in breach of the law."
Kevin Coyne, national officer of Unite union has backed plans for the first in a fleet of new nuclear power stations. He said:
The construction of Hinkley Point C will create thousands of skilled construction jobs for the next five years, and around 800 jobs in the operation of the power station over the next 60 years.
We hope Hinkley Point C is just the first in a fleet of new nuclear power stations which would create jobs in construction for the next 20 years. Nuclear is a crucial part of a balanced energy policy, to stop lights going out.
The first of a planned fleet of nuclear reactors in the UK could be given the go ahead today.
Energy Secretary Ed Davey is expected to announce whether he will grant consent for energy giant EDF to build a nuclear power plant at Hinkley Point C in Somerset.
According to EDF, the plant's two nuclear reactors would be capable of producing enough energy to power five million homes, or seven per cent of the UK's electricity.
The decision to go ahead with construction depends on a deal being negotiated with the Government on the "strike" price paid for electricity generated by the plant.