Whether the new plants, known as Hinkley Point C, get the green light and, if so, how well they work out may have a huge effect on the future of the nuclear energy industry across the world. The shock waves from the Fukushima disaster in Japan in 2011 are still being felt. China is going ahead with its ambitious nuclear program, but Germany is abandoning nuclear power, and many countries that were once eager to harness the atom to meet their surging electricity needs are now wary, according to Mark Hibbs, a nuclear analyst at the Carnegie Endowment for International Peace.

France has long been a leading proponent of nuclear power, but the construction of early versions of a new generation of French-designed reactors called EPRs, which will be used at Hinkley Point, has hit snags and huge cost overruns at Olkiluoto in Finland and Flamanville in France. EDF is building two other EPRs at Taishan in China with China Guangdong Nuclear Power.

EDF now operates eight nuclear plants in Britain, including one at Hinkley Point. The company hopes that success there will persuade not only Britain but other countries to sign up. Even EDF and its 20 percent partner, the British utility Centrica, say they cannot afford the huge capital costs of building a new nuclear plant without some assurances.

Soaring cost estimates of as much as £7.5 billion, or $11.7 billion, for the plants mean the companies would not make a sufficient return on their investment at current electric prices, they say. The government now plans to guarantee revenue for nuclear plants through a mechanism by which they would be paid additional sums if electricity rates were below a certain floor. Analysts think that strike price will need to be at least £100 per megawatt-hour — about double the current British rate. The government says this would not be a subsidy, but it looks like one to critics.

“You have to get the marketplace to a point where you have confidence that you can get a return on your money,” Mr. Cann said, while declining to put a figure on costs.

In a blow to the government, the German utilities RWE and E.On said last spring that they would sell their stakes in another nuclear consortium, Horizon. A British utility, SSE, had previously pulled the plug, citing unquantifiable costs.

The government is now hunting for replacements. Because there is no major British nuclear supplier, companies from abroad need to play major roles. Among the candidates are EDF’s partner, Guangdong Nuclear, and another Chinese company. The thinking — perhaps wishful — is that helping finance the British program would provide the Chinese industry with a high-profile opportunity to establish its credentials as a nuclear exporter.