EDF Energy has warned that Hinkley Point C will cost at least £1.5bn more than first thought and could be delayed by up to two years.
The French energy giant issued a statement following a review of the time and costs associated with the Somerset nuclear new-build project.
The review found that the costs were now estimated at £19.6bn – up £1.5bn on 2015 prices.
EDF attributed this to design changes to meet regulatory demands; the volume and sequencing of the work; and introduction of new supplier contracts.
The energy giant said its projected rate of return on the project was now 8.5 per cent, down from 9 per cent in 2015.
It added there was a risk of delays to the project of 15 months for the first phase and up to nine months for the second phase, which could cost an additional £700m.
Hinkley’s first phase is expected to be complete by the end of 2025.
The National Audit Office last month slammed the government’s signing of a deal to support the construction of the nuclear plant, warning that it had locked consumers into a “risky” and expensive project.
Earlier in June, EDF Energy confirmed that its chief executive Vincent de Rivaz would step down in October after 15 years in the post.
In March, EDF issued a progress report following the first permanent concrete pour on the nuclear scheme.
Construction of Hinkley Point C – approved by the government last year – will involve three million tonnes of concrete and 230,000 tonnes of steel.