French energy giant EDF learned the British government wanted to delay its final decision on the Hinkley Point nuclear power plant the day before its board met to approve the plan, according to an email from its CEO seen by AFP.

EDF approved the 18 billion pound project ($24 billion, 21 billion euro) plan to build Britain's first new nuclear plant in decades -- a project that had deeply divided the company's directors -- on July 28.

But the British government immediately said it would wait until the autumn before taking a final decision.

In an email to EDF's executive committee, CEO Jean-Bernard Levy said he learned "late on the evening of Wednesday 27" that British Prime Minister Theresa May "was asking for a little more time, without reassessing the project, without giving the date when it could be signed," and "that she would not discuss the matter".

"We therefore cancelled the preparations for the signature (ceremony)," he wrote in the email, sent on Tuesday evening.

A ceremony to sign the deal on Hinkley Point had been planned in Britain on July 29, the day after the EDF board met to approve it, Levy said.

"So when the board voted, the afternoon of Thursday 28, we knew the ceremony would not go ahead the next day," he wrote.

But he said the company was not aware of the content of the British government's statement issued in the hours after the EDF board decision.

Britain's business and energy minister Greg Clark said the government would "consider carefully all the component parts of this project and make its decision in the early autumn".

May must approve the deal before it can go ahead.

The French government has been keen to get Hinkley Point approved as it sees the project as crucial for the long-term viability of France's nuclear industry, which employs 220,000 people.

Previous British governments have also been in favour because the reactors will cover up to seven percent of Britain's electricity needs while helping the government meet its CO2 emissions targets.

But British support is not unanimous, and criticism focuses on the growing difference between an electricity price guarantee for EDF, subsidised by the British taxpayer, and current falling energy prices.

There have also been national security concerns about Chinese involvement in the project -- Beijing has a one-third stake in the plan.

Contacted by AFP, EDF declined to comment.