British trade unions criticised the government on Friday for delaying its final decision on the Hinkley Point nuclear power plant, seen by British media as backtracking on the project.

"Theresa May's decision to review the go-ahead on HPC is bewildering and bonkers," said Justin Bowden, the GMB union's national secretary for energy, about Britain's new prime minister.

"After years of procrastination, what is required is decisive action not dithering and more delay," he said.

Business and energy minister Greg Clark on Thursday said that the government "wanted time to study the details of the deal" and would not give a decision until early autumn.

Kevin Coyne from Unite, Britain's biggest trade union, said jobs could be lost and the delay could penalise economic growth.

"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.

After years of discussion, French energy giant EDF on Thursday approved the PND 18 billion project ($24 billion, 21 billion euros) for two EPR nuclear reactors in Somerset in south-west England.

EDF chief executive Jean-Bernard Levy on Friday said at the company's earnings announcement: "I don't doubt the support from Theresa May's British government".

French unions have re-asserted their opposition to a project that they say risks plunging the group in financial difficulties.