Thomas Piquemal told a French parliamentary committee that he quit the energy giant after management rejected his calls for a final investment decision to be postponed until at least 2018.

Mr Piquemal said: “In January 2015, I proposed to negotiate a three-year delay with our client because we reasoned that it would weigh too heavily on EDF’s balance sheet.”

He added that plans to build the Somerset plant posed a “major construction risk” and that EDF was gambling up to 70 per cent of its equity on unproven technology.

His comments come just a week after the French government confirmed that a final investment decision on the £18bn project would not be made before September. It also revealed plans to raise £3.1bn through a rights issue to cover the cost of its future operations.

Mr Piquemal said that he could not sign off on a decision that would see EDF follow the same route as nuclear firm Areva, where the company would have to ”recapitalise a few months before defaulting on payments”.

Last year, the French government was forced to recapitalise Areva ahead of selling its reactor business to EDF.

When it goes ahead, Hinkley is set to use Areva’s EPR reactor.

The reactor has so far been used in three EDF plants: in Finland; in China; and in its native France.

One of those plants – Flamanville in northern France – is running six years behind schedule and €7bn (£5.2bn) over budget.

The Finnish Olikuluoto 3 plant is now 10 years behind schedule and €5bn (£3.7bn) over budget.

The Chinese Taishan 1 plant has been under construction since 2009 and is expected to start up in the first half of 2017, while Taishan 2 is scheduled to begin operating by the end of that year.

EDF declined to comment on Mr Piquemal’s comments.