Britain's government has said it will launch a new review into a controversial project to build two new nuclear reactors led by French utility EDF, the country's first new nuclear plant in decades.

EDF's board narrowly voted to proceed with the Hinkley Point project on Thursday.

But in a surprise move, the government of Britain's new Prime Minister Theresa May said it wanted to give the project further consideration.

"The UK needs a reliable and secure energy supply and the government believes that nuclear energy is an important part of the mix," Business and Energy Secretary Greg Clark said in a statement shortly after EDF gave its go-ahead to the project.

"The government will now consider carefully all the component parts of this project and make its decision in the early autumn."

The £18 billion ($24 billion) nuclear reactors carry commercial risks for both France and Britain. EDF will assume the up-front costs, which unions say could jeopardise the firm's survival, while Britain has committed to pay a price twice current market levels for the power generated by the plant.

EDF said in a statement its board had made the final investment decision on the project and had given chief executive Jean-Bernard Levy the authority to sign all necessary contracts, but it did not detail the voting tally on the board.

A source with direct knowledge of the situation told Reuters that following the resignation of board member Gerard Magnin in protest over EDF's strategy ahead of the meeting, the remaining board members had approved the project, with 10 members voting in favour and 7 voting against. - Reuters