The cost of building the new nuclear power station at Hinkley Point has risen by £1.5 billion, it has been announced.
French energy giant EDF said it will now cost £19.6 billion to build the site in Somerset.
The news follows a review of the costs and timetable of the project, undertaken after EDF's final investment decision last September.
A statement said: "The milestone for the first nuclear safety concrete for the building of Unit 1, scheduled for mid-2019, is confirmed, assuming that the final design, which is on a tight schedule, is completed by the end of 2018.
"Project completion costs are now estimated at £19.6 billion in 2015 sterling, an increase of £1.5 billion in 2015 sterling, compared to previous evaluations.
"This estimate includes successful operational action plans, in partnership with suppliers.
"The estimated additional costs result mainly from a better understanding of the design adapted to the requirements of the British regulators, the volume and sequencing of work on site and the gradual implementation of supplier contracts."
EDF said there will be no financial impact on UK consumers of the increased costs.
It added there was a risk of deferral of 15 months for the power station's Unit 1 and nine months for Unit 2, but it was sticking to the objective of 2025 for start-up.
John Sauven, executive director at Greenpeace UK, said: "Hinkley is already over time and over budget after just a few months of building work.
"Today's news is yet another damning indictment of the Government's agreement to go ahead with this project.
"This year's school leavers will still be paying for Hinkley when they approach their pension age. And now it looks like they will be paying for the most expensive object on earth for even longer."
A spokeswoman for the Department for Business, Energy & Industrial Strategy said: "As the developer has made clear, the project remains on track to meet its first major milestone in 2019.
"The UK Government negotiated a competitive deal which protects consumers and ensures that all of the cost of construction, including any overruns, sits with the contractor.
"Hinkley Point C will be the first new nuclear plant in a generation. This was an important strategic decision to ensure that nuclear is part of a diverse energy mix in the UK.
Consumers won't pay a penny until Hinkley is built; it will provide clean, reliable electricity powering six million homes."