The Government's energy policies are coming under increasing criticism after the chief financial officer of power giant EDF resigned, casting fresh speculation over its plans to build a new nuclear power station at Hinkley.

Thomas Piquemal is believed to have stepped down because of concerns that a final decision on investment for the £18 billion project in Somerset was being made too soon, potentially threatening EDF's financial position.

The company, which is 85% owned by the French government, recently gave assurances that it was close to making a decision on the proposed Hinkley Point C project.

But a series of delays have led to calls for the Government to review its energy plans.

John Sauven, director of Greenpeace, said: " Alarm bells should be ringing deafeningly loudly in the offices of the French and UK governments this morning.

"The Chief Finance Officer's decision to quit over EDF's apparent commitment to push ahead with the controversial Hinkley nuclear power deal should be of huge concern.

"If the finance chief thinks the project will be a disaster, the optimism from both governments that the deal will be imminent is irrational.

"The UK Government urgently needs a 21st century plan to boost our home-grown renewable energy which is being sidelined because the Government is focusing on this nuclear white elephant."

Shadow energy secretary Lisa Nandy said: "This power station is absolutely central to the Government's strategy for keeping the lights on and meeting Britain's international commitments on climate change. With growing scepticism over whether it will now be built, ministers must tell us: what is their plan B?"

The company said Mr Piquemal will be replaced by Xavier Girre, who joined EDF last year as chief finance officer for France.

After a summit in France last month, Prime Minister David Cameron and French president Francois Hollande issued a communique that said there had been "major progress" in recent months "with a view to confirming the project".

EDF also said it will extend the life of four of its UK nuclear power stations by between five and seven years.

Asked about Mr Piquemal's reported departure, David Cameron's official spokeswoman said: "I'm not going to speculate on the resignation of one individual. That is a matter for EDF.

"We continue to fully support the project and President Hollande said himself on Thursday afternoon that it has the full support of the French government.

"The French government are in discussions with EDF on this. They've been clear that they fully support this, and now we wait for the next stage, which is the financial investment decision. The discussions under way are regarding support from the French government."

Phil Whitehurst, national officer of the GMB union, said: "The UK Government should now be considering a move to Plan B. The Nuclear Decommissioning Authority should be redesignated as the Nuclear Development Authority and take over responsibility for the project - which has to go ahead.

"The UK construction industry and its supply chain simply cannot be left hanging in limbo any longer with regards to the final investment decision of Hinkley Point C, where infighting inside the EDF board has now created yet another high-powered resignation."