EDF has reignited fears over its troubled new nuclear project at Hinkley Point C after admitting it will cost the French energy giant over £20bn and could be delayed by almost two years to 2027.

An internal review of the project by senior executives at EDF reignited fears that the state-backed group will not be able to deliver Hinkley in line with the protracted timeline or its multi-billion pound budget.

It revealed that the cost of building the UK’s first new nuclear plant in a generation had climbed by £1.5bn in two years to £19.6bn after a string of delays to the project. A further delay of fifteen months could add a further £700m to the spiralling costs to push them over £20bn.

The Somerset-based reactors are a key pillar of the Government's plan to clinch investment in a clean, secure power system. The 3.2GW plant was expected to start delivering power to the national grid in 2025 but could now be delayed to 2027, a decade after the first start date proposed by EDF.

In 2007 Vincent de Rivaz, the UK chief executive, said he hoped the new Hinkley Point reactors would provide electricity for Britons to cook their Christmas turkeys in 2017 but this time frame has slipped repeatedly through years of political wrangling over its costs.