PARIS (Reuters) - EDF <EDF.PA> Chairman and CEO Jean-Bernard Levy had no prior knowledge of Britain's decision to review the Hinkley Point nuclear project and will sue a French union for suggesting otherwise, the French utility said.

EDF's board approved the 18 billion pound ($24 billion) nuclear plant project on July 28, but hours later the government of new British Prime Minister Theresa May said it wanted more time to study the plan and would decide on it in the autumn.

In a statement late on Friday, EDF said Levy would take legal action against the Sud Energie union for alleging he had lied to reporters by saying he had not known before the board meeting that Britain would conduct a fresh review.

"Reading the entire internal email sent on August 2 by the Chairman and CEO of EDF to members of the executive committee confirms unambiguously that when the Company's Board of Directors was held, EDF and its Chairman had no knowledge of the intention of the British government to conduct a further review of the Hinkley Point project," the company said.

"All that was known before the press statement issued by the British government on July 28 was that the signing ceremony originally proposed for Friday, July 29, would be postponed," EDF said.

"This potential date of signature had not been confirmed, and therefore had not been communicated either to the board nor the market. There was therefore no requirement to communicate its postponement."

Sud Energie stands by its comments on the issue which were made in an email on Friday to several thousand EDF employees, Jerome Schmitt, a member of the union's national bureau, told Reuters.

EDF said Levy and EDF would also take legal action against any other parties making claims like those of Sud Energie.

EDF's unions have said the Hinkley Point project is too big and jeopardizes the company's survival.

The project also led to the resignation of the group's former finance chief earlier this year while a board member quit on the day of the investment vote.

A Paris court on Friday upheld the EDF board's investment decision on the Hinkley Point nuclear project in Britain, rejecting a challenge by the group's works council.

A separate legal challenge by the works council, seeking to obtain the release of confidential documents relating to Hinkley Point, is due to be heard on Sept. 22.

EDF and Chinese partner China General Nuclear, which holds a one third stake in the project, are responsible for the project's construction costs, while Britain would pay a minimum price for the power generated by the plant for 35 years.

($1 = 0.7651 pounds)

(Reporting by Gus Trompiz. Editing by Jane Merriman)