The first new UK nuclear power station in a generation faces a fresh delay after the Government said it will not make a decision until the autumn.
After years of delay, a board meeting of energy giant EDF in Paris voted by 10-7 to give the go ahead for the £18 billion Hinkley Point power station.
The vote was closer than expected but was warmly welcomed by business groups and trade unions, with 25,000 jobs now set to be created.
Documents were expected to be signed on Friday and senior EDF officials were due to give interviews.
But the Government pulled back from any signing ceremonies, prompting fresh question marks about the start of the much-delayed project.
Business and Energy Secretary Greg Clark said: "The UK needs a reliable and secure energy supply and the Government believes that nuclear energy is an important part of the mix.
"The Government will now consider carefully all the component parts of this project and make its decision in the early autumn."
Mr Clark only returned from a three-day trade visit to Japan earlier on Thursday and is now expected to spend time studying details of the EDF decision.
Opponents seized on the Government statement to call on ministers to halt the project.
John Sauven, Greenpeace's executive director, said: "Theresa May now has a chance to stop this radioactive white elephant in its tracks.
"She should look at the evidence and see that this deal would be a monumental disaster for taxpayers and bill payers. The UK needs to invest in safe, reliable renewable power.
"The Government should be embracing new innovative technologies that are powering Northern European countries already and coming down in price every year.
"We don't want to be left behind and locked into an old-fashioned nuclear power plant that isn't working anywhere in the world and isn't fit for the 21st century."
EDF's chief executive Vincent de Rivaz was expected in Somerset on Friday morning alongside senior company officials to give interviews about the project. But following the government statement it emerged that no interviews would be given.
Conservative MP Zac Goldsmith tweeted: "It's hard to imagine a worse deal than Hinkley Point project. If this pause equals a genuine rethink by Government, that's very good news."
There was speculation that the Prime Minister was involved in the move to allow time to study the details before any deal is signed and sealed.
Critics believe the Government has been stung by criticism of the amount of money EDF will be paid for generating power from Hinkley - £92.50 per unit of electricity generated.
Unite national officer for energy Kevin Coyne said the decision by EDF was historic and urged the Government to sign the contracts as a matter of urgency.
"Any further delay or backsliding would hold back the economic boost and the accompanying creation of thousands of skilled jobs that this major infrastructure project will bring," he said.
"Our members are shovel ready to start work on the country's first nuclear power station for a generation and British companies are at the ready to build and supply this £18 billion project."
China General Nuclear, which has a stake of a third in the Hinkley project, said: "We respect the new government's need to familiarise itself with a project as important to the UK's future energy security as Hinkley Point C and we stand ready to help the Government in this respect.
"CGN remains committed to delivering this much needed nuclear capacity with our strategic partners EDF, and providing the UK with safe, reliable and sustainable energy.
Hinkley will provide 7% of the UK's generation needs for 60 years and is scheduled to begin generating power in 2025, a lot later than the promise made by Mr de Rivaz in 2007, who said Britain would be cooking Christmas turkeys on new nuclear power by 2017.