The French electricity giant EDF has thrown the British government’s energy strategy into disarray by reportedly delaying – possibly until next year – a decision on whether it will build a new £18bn nuclear power station at Hinkley Point in Somerset.

Jean-Bernard Lévy, the head of EDF, has bowed to pressure from unions and senior company engineers and agreed to seek a fresh opinion from the company’s union-management consultative council, the respected French newspaper Le Figaro reported.

EDF said it could not immediately confirm the report. Sources in the company told the French newspaper that the consultation process would take several months and that no decision on whether to go ahead with its involvement in Hinkley Point – expected to supply eight per cent of British slectricity by 2025 – would be made before next year.

An internal report to the EDF board warned in February that it would be impossible for technical reasons to complete the two “new generation” nuclear reactors at Hinkley within the nine-year timetable. The report also suggested that the project could be financially disastrous for EDF, despite a commitment by the UK government to pay double the market rate for Hinkley’s electricity.

Although China has agreed to invest £6.2bn in Hinkley Point, EDF has failed to find other backers, leaving it responsible for two thirds of the cost. Problems with the bulding of similar high-pressure water reactors in Finland and Normandy have led EDF unions and senior executives to recommed a three-year delay – until a new generation of technology become available.

But Paris and London are reported to have applied intense pressure on EDF to go ahead immediately.

The British government would face huge embarrassment if Hinkley Point, intended as the first of three new mega power stations, was abandoned or postponed. In October last year, China agreed, amid much fanfare in London and Beijing, to invest £6.2bn in the project.

In September, the Chancellor George Osborne said Hinkley Point was a central part of the government’s strategy to “make sure the lights stay on”. “The current generation of nuclear power stations are coming to the end of their life. That’s going to create a very big hole in our base electricity supply unless we do something about it,” he told a House of Lords committee.

John Sauven, director of Greenpeace, which has campaigned against the reactor, told The Independent: “Delays to EDF making a decision about whether to invest in Hinkley are nothing new. So much so that it’s been 14 months since it was first said that the decision would be coming imminently. But this latest delay from EDF is different.

“President Hollande, the French Economy Minister and EDF’s chief executive have all very publicly promised the UK government a final decision before the 12 May. Backtracking on this pledge now is symbolic of the utter mess that EDF is in.

“But even if they could agree a finance package, it could be declared illegal state aid by the European Commission. This may now be the sign that the entire project is coming to a grinding halt and the UK government urgently needs to back renewable energy as a more reliable alternative.”

“French utility EDF (EDF.PA) has delayed the final investment decision for its Hinkley Point nuclear project in Britain until after its May 12 shareholders’ meeting to allow time to consult its works council, two sources familiar with the situation told Reuters.

Greenpeace has written to George Osborne warning him not to allow the Hinkley Point C nuclear project to proceed until the European commission approves further planned support from the French state.

The letter, which is signed jointly with the energy supplier Ecotricity, follows legal advice that plans for state help from France’s government to enable EDF to continue with the reactor scheme could break European competition rules.

The legal opinion was given to Greenpeace by three competition barristers from Monckton Chambers in London and came as EDF held a board meeting on Friday in Paris to discuss once again the controversial £18bn project in Somerset.

“The only way Hinkley can be kept alive is on the life support machine of state aid. EDF, if it is to stay in business, needs a new vision which is not looking backwards,” said John Sauven, executive director of Greenpeace UK.

“The UK government needs to stop penalising the UK renewable energy industry in favour of propping up an ailing state-owned nuclear industry in France.”

Dale Vince, founder of Ecotricity, said it was time for everyone to realise that it was the end of the road for Hinkley Point.

“Illegal state aid is one thing, and we’ll work with Greenpeace to challenge that if it happens, but it’s not just financial issues, there are technical problems with Hinkley Point too – EDF are yet to build one of these reactors and their first two attempts are, between them, 16 years late and billions over budget,” he added.

The letter was also sent to Amber Rudd, the energy and climate change Secretary. Rudd and Osborne have been key figures in trying to steer investment into new nuclear plants.

EDF, which is 85% owned by the French state, is struggling against a mountain of debt and has told ministers it will not build Hinkley unless it obtains help from France’s government.

The country’s economy minister, Emmanuel Macron, has talked about taking future dividends in shares rather than cash and a range of other options to lessen the financial burden on EDF.

It is these proposals that the London barristers believe would need clearance from Brussels, a process that would subject Hinkley to further delays.

Molly Scott Cato, Green MEP for the area covering the plant, said: “The numbers for the Hinkley deal have never stacked up and it is clear that the commercial case for this white elephant is dead. We have now a political battle where the stakes for both the UK and France are just too high to admit failure. But we cannot let this override EU rules on state aid or fair competition.”