Plans for a multi-billion pound new nuclear power station have been suspended, delivering a huge blow to the industry and putting thousands of jobs at risk.
Japanese firm Hitachi announced it was not continuing with work already under way at Wylfa on Anglesey in North Wales.
The company said it had made "strong progress" on the project, but had not been able to reach agreement on financing and associated commercial arrangements.
Thousands of jobs were set to be created building Wylfa and hundreds of employees would have been based at the site.
The decision will cost them approximately 300 billion yen (£2.14 billion), Hitachi said in a statement.
Duncan Hawthorne, chief executive of Hitachi’s nuclear business, Horizon Nuclear Power, said: “We have made very strong progress on all aspects of the project’s development, including the UK design of our tried and tested reactor, supply chain development and especially the building of a very capable organisation of talented and committed people.
“We have been in close discussions with the UK Government, in co-operation with the government of Japan, on the financing and associated commercial arrangements for our project for some years now. I am very sorry to say that, despite the best efforts of everyone involved, we’ve not been able to reach an agreement to the satisfaction of all concerned.”
Hitachi said it will also suspend work on another site, in Oldbury in Gloucestershire, “until a solution can be found”.
“In the meantime, we will take steps to reduce our presence but keep the option to resume development in future,” said Mr Hawthorne.
“We will begin consultation on the implications immediately with our staff who have shown extraordinary talent, resilience and determination to take this complex and exciting project to this stage.
“We will also engage closely with the many international and UK-based stakeholders who have strongly supported the project’s development, especially our lead host community of Anglesey in Wales, represented by the Isle of Anglesey County Council and Welsh Government, and the key representatives around Oldbury.”
A Business Department spokesman said: “As the Business Secretary set out in June, any deal needs to represent value for money and be the right one for UK consumers and taxpayers.
“Despite extensive negotiations and hard work by all sides, the Government and Hitachi are unable to reach agreement to proceed at this stage.
“This Government is committed to the nuclear sector, giving the go-ahead to the first new nuclear power station in a generation at Hinkley Point C, investing £200 million through our recent sector, which includes millions for advanced nuclear technologies.
“We are also reviewing alternative funding models for future nuclear projects and will update on these findings in summer 2019.”
Hitachi’s move follows a decision by Toshiba not to go ahead with a nuclear power station at Moorside in Cumbria.
Justin Bowden, national officer of the GMB union, said: “Hitachi’s announcement, coming so soon after the Moorside fiasco, raises the very real prospect of a UK energy crisis.
“As coal is taken out of the equation in the next few years and the existing nuclear fleet reaches the end of its natural life after 50 years, decisions are already long overdue for construction to be completed in time and not leave the country at risk of power cuts or reliant on imported electricity, much of it from unreliable regimes.
“While the Government has had its head up its proverbial backside over Brexit, vital matters like guaranteeing the country’s future energy supply appear to have gone by the wayside.”
Hitachi has already spent over one billion on the project, which would have been expected to cost around £15 billion on completion.