The company, part of a French-Chinese consortium awarded the two-reactor project in 2016 despite criticism from green groups and cost warnings from experts, warned that costs were "now estimated at between 21.5 and 22.5 billion pounds (24.4-25.5 million euros/$26.8-28.1 million" at 2015 sterling rates.

That equates to a rise of between 1.9 and 2.9 billion pounds over previous estimates.

The project has already been dogged by delay and cost hikes. Following a review, EDF warned two years ago of a pound1.5 billion overrun and delays of up to 15 months.

EDF blamed the rising costs largely on difficult ground excavation conditions.

But it insisted the new estimation would not impact either consumers or British taxpayers.

The Hinkley Point C project, built in the southwestern English county of Somerset, is supposed to provide seven percent of Britain's power needs, according to the government.

But critics have focused on the proposed design, which uses a novel EPR reactor that has run into huge problems of cost overruns and delays at sites in France and Finland.

They have also questioned an electricity price guarantee to EDF of pound92.5 for every megawatt hour of power produced by Hinkley over the following 35 years, rising with inflation, regardless of falling energy prices.

Britain's National Audit Office (NAO) has also long criticised the scheme, saying the government has "locked consumers into a risky and expensive project with uncertain strategic and economic benefits".

The project, scheduled under the deal to start producing electricity in 2025, has a projected operational lifetime of 60 years.

Heavily-indebted EDF, mainly owned by the French government, is funding around two-thirds of the cost and its Chinese partner the remainder.

Similar problems to those at Hinkley have also hit EDF's reactor project at Flamanville in western France, though the firm has successfully launched two reactors with Chinese partners in the Chinese city of Taishan.

jmi/pn/cw/bp

EDF - ELECTRICITE DE FRANCE

AREVA