It is the four reactors being built for nuclear power stations outside Waynesboro, in Georgia, and Jenkinsville, South Carolina, by the company’s US subsidiary Westinghouse that have left the Japanese corporation facing an annual loss of £7.37bn.

Construction work on the units has run hugely over budget and over schedule, casting a shadow over two of the biggest new nuclear power station projects in the US for years.

Events came to a head last month when Westinghouse was forced to file for bankruptcy protection to limit Toshiba’s losses.

Experts said the delays and cost problems were due to America’s lack of recent experience in building atomic power plants.

“I don’t think it is necessarily because of an inherent issue of US skills but rather the lack of practice,” said Richard Nephew, a professor at the Centre on Global Energy Policy, Columbia University. “There simply have not been as many new reactor builds in the US and this has reduced the overall pool of skilled labor, no question.”

The absence of a mass production supply chain, due to the small number of the Westinghouse-designed reactors being built, played a part too, he added. Regulatory issues had also delayed construction. …

Richard Morningstar, chairman of the Global Energy Centre at the international affairs thinktank Atlantic Council, said: “What is happening to Westinghouse and Toshiba only emphasises the need to double down on research on new, safe, nuclear technologies, such as small modular reactors. If we do not do so in the US, leadership will be ceded to other countries.” …

One such aspiring atomic leader is the UK, where the government wants to build a new generation of nuclear power stations to help satisfy the country’s power needs for decades to come.

But there are obvious parallels between the two countries on the issues of recent experience and supply chains. The UK has not completed a new nuclear power station since Sizewell B on the Suffolk coast started generating power in 1995.

EDF, the French state-owned company which has started pouring concrete at Hinkley Point in Somerset, where it plans to have two reactors operational by 2025, maintains it has had plenty of recent practice.

The EPR reactor design for Hinkley is the same as that for the reactors it is building in Finland, and at Flamanville, in France, though both of those are running late and over budget.

The other new nuclear projects proposed around the UK, all by foreign companies, look less certain and all are still years from construction starting in earnest.

Toshiba said this week it would consider selling its shares in the consortium behind another plant planned at Moorside, in Cumbria, which would utilise three of the same AP1000 Westinghouse reactors being built for the two crisis-hit US plants.

The South Korean power company Kepco last month expressed an interest in buying into the project, and the business secretary , Greg Clark, went to South Korea last week for talks on collaboration on nuclear power. …

Justin Bowden, GMB national secretary, said: “The big moral of the story is what on earth we are doing as a country, leaving our fundamental energy requirements to foreign companies or foreign governments?”

While the government has argued that it has plans in place to keep the lights on if new nuclear projects do not materialise, others said the deepening crisis at Toshiba this week showed the need for ministers to consider a new energy policy.

“It’s time to come up with a new plan A,” said Paul Dorfman, of the Energy Institute, at University College London, who believes the Moorside project is dead. “It’s time for a viable strategy that talks about grid upgrades, solar, energy efficiency, and energy management.”

A report published on Thursday highlighted another alternative: a U-turn on the Conservative party’s manifesto commitment to block new onshore windfarms. Analysis for the trade body Scottish Renewables suggested wind turbines on land had become so cheap they could be built for little or no subsidy, compared to the lucrative contract awarded to EDF for Hinkley.