When Rishi Sunak visited Barrow-in-Furness on Monday he said the Cumbrian town was “mission critical for our country” because of its role building four new nuclear submarines to carry the UK’s nuclear weapons. If you believe Sunak’s erstwhile ally, Dominic Cummings, then that mission faces serious problems. Cummings, once Boris Johnson’s most powerful adviser, said this month – in characteristically aggressive terms – that spiralling costs were making a mockery of the government’s budget plans. He wrote on X: “the nuclear enterprise is so fkd [sic] it’s further cannibalising the broken budgets and will for decades because it’s been highly classified to avoid MPs thinking about it.” But the scale of the issue makes it hard to ignore. The government re­iterated last week that the four new Dreadnought class submarines would cost £31bn plus a £10bn “contingency”. But the Nuclear Information Service (NIS), a monitoring group, said in 2019 that the full cost of the nuclear weapons programme between 2019 and 2070 could be £172bn, when including new warheads and running costs. Costs are also increasing rapidly, as the government has prioritised replacing the existing Vanguard submarines on time rather than on budget. (The Vanguard boats launch Trident nuclear missiles – like the one that crashed into the sea during a test last month.) The Ministry of Defence puts the cost of the programme to replace the UK’s nuclear weapons at £118bn over the next decade. That is already £8bn more than the Treasury has forecast, suggesting something may have to give elsewhere. The National Audit Office, a government watchdog, found in December that forecasts of costs of the MoD’s Defence Nuclear Organisation had risen by £38.2bn in the past year. However it is counted, hugely costly delays and overruns, plus inflation, mean a reckoning is overdue on the costs of Britain’s nuclear submarines. “They don’t have very many good options,” said David Cullen, director of the NIS. He said the problems appeared so intractable that it could affect the UK’s continuous at-sea deterrence – the longstanding policy of always having a nuclear-armed submarine gliding silently under the waves in case of attack. “It would be much better for them to make a conscious decision to stop having constant patrols, rather than having it forced on them,” he said. Nuclear submarines are among the most complicated machines ever built. They sustain 132 humans deep beneath the oceans, needing to surface only when its crew runs out of food – or runs out of patience during months without daylight. The Labour party, eyeing power in an imminent election, has a decision over whether to confront the problem head-on – and add billions to already constrained budgets – or to continue with the sticking-plaster approach. One thing Labour has said it will not do – to the chagrin of campaigners particularly aligned with the left of the party – is accept the UK’s diminished role in world affairs by scrapping the nuclear deterrent. David Lammy and John Healey, shadow foreign secretary and defence secretary respectively, wrote in September that “with Keir Starmer, our commitment to Nato and the UK’s nuclear deterrent – maintained on behalf of Nato allies – is unshakeable”. Some in the defence industry believe Labour could, if elected, choose to launch an inquiry into the entire nuclear defence enterprise – which might allow it to blame the current government and help ease the blow from a big hit to its budget. However, a Labour source said the lack of visibility into classified plans meant it was not yet able to work out a detailed strategy. One way to help government finances might be to share costs. Under the new – and increasingly controversial – Aukus alliance, Australia will receive nuclear weapons technology from the UK (with the blessing of the US, which originally bestowed the city-destroying abilities on Britain). The Aukus programme is split into two “pillars”. Pillar one is centred on helping Australia acquire conventionally armed, nuclear-powered submarines. The second part is more techy, focusing on speeding up cooperation of specific technologies – including artificial intelligence, cyber work, quantum computing and hypersonic weapons.) In 2022, the second pillar of the pact was extended to allow the trilateral partners to develop hypersonic weapons in response to Russia’s use of the deadly high-speed missiles in airstrikes in Ukraine. The French defence giant Thales, a supplier of sonar and light-sensing masts, is expected to pick up work as the “eyes and ears” of the submarines. Its UK boss, Alex Cresswell, told the Observer: “Pillar one of Aukus is a once-in-a-generation event that is extremely significant for the industry as a whole. I recruit graduates on the basis of it.” Cresswell adds: “The rate of the submarine part is being driven by the design work on the submarine after Dreadnought … that early design work is being placed now and we’re involved in it.” Yet it is unlikely that Aukus will help to fill the Dreadnought black hole. Immediate manufacturing problems appear to be the problem there, which will not be helped by the promise of future work for submarines built after Dreadnought, according to NIS’s Cullen. Meg Hillier, a Labour MP who heads the public accounts committee, said that budgets have been blown because of the government’s “stop/start approach to defence procurement” and “a lot of optimism bias” in plans. She said the nuclear submarine budget is one of the “big nasties” lying in wait for a future government. It is an ominous threat lurking under the surface for the next prime minister.