The French energy giant was fined €1.5m (almost £1.3m) for “industrial espionage”, after a hacker spied on Greenpeace’s anti-nuclear campaign in 2006.

EDF, which runs eight nuclear power stations in the UK, is a French company that also runs the French electricity industry.

The court in France was told that EDF wanted advance warnings of Greenpeace’s plans to disrupt the construction of a new nuclear power station in Normandy.

EDF, however, claimed the hacker had been hired without its knowledge by an industrial intelligence company. EDF is reportedly now considering an appeal.

Adelaide Colin, communications director for Greenpeace in France, said the decision “sends a strong signal to the nuclear industry: no-one is above the law”.

The court also sent two employees of security firm Kargus – who EDF are said to have enrolled to carry out the spying – to jail, and ordered EDF to pay Greenpeace the equivalent of £428,000 in damages.

The head and deputy head of EDF’s nuclear security operation, Pascal Durieux and Pierre-Paul Francois, were handed three-year sentences.

EDF is hoping to build four new nuclear reactors in the UK.