Cash-strapped EDF could have to find an additional £2bn to build the Hinkley Point C nuclear power plant.
There's rising pressure at the French utility giant over whether its already strained balance sheet will be able to shoulder the hugely expensive project.
An independent report regarding the controversial project seen by the Times claims the updated cost could be as high as €25.3 billion (£19.8 billion).
This is because Areva, the company behind the nuclear reactors which will be used, is repricing its technology ahead of the final investment decision in early May.
Michel Degryck, managing partner of the Paris-based corporate finance advisory Capitalmind which conducted the analysis, said: "We understand that a number of costs were probably underestimated when they did their last pricing [of the reactor] in 2013."
"They will have to take into account new costs . . . The cost of the project could rise by 10 per cent."
EDF refuted the report, with a spokesman saying that the contracts are signed and won't change.
Yesterday, Christian Taxil, EDF board member for managers’ union CFE-CGC, wrote to employees saying he would vote against plans to build Hinkley citing current energy prices, technical issues with the nuclear reactors it plans to build and the company’s weak balance sheet.
Thomas Piquemal, EDF’s finance director, resigned last month while warning that Hinkley could put the company in financial jeopardy.
French economy minister Emmanuel Macron has since pledged fresh financing for the project.
Hinkley is the UK's first nuclear power plant in decades and the world's most expensive atomic energy project ever. It's is due to start generating in 2025, and is expected to provide seven per cent of the UK's electricity once operational.