An enthusiastic Rishi Sunak has told ministers to expect a positive outcome next week when he travels to San Diego to unveil a deal to supply nuclear-powered submarines to Australia as part of the Aukus pact with the US. Multiple sources said they believed the UK had succeeded in its bid to sell British-designed nuclear submarines to Australia, a deal that will safeguard the long-term future of the shipyard at Barrow-in-Furness. A senior minister said Sunak had told colleagues he was delighted by the outcome of the negotiations, which have been going on for 18 months and have presented Australia with a choice between a British or a US design, based on the existing Astute or Virginia class submarines. “The deal has definitely gone our way. The prime minister was buzzing about it when he told ministers, smiling and bouncing on the balls of his feet,” the minister said. A second source outside government with knowledge of the talks said they had also been told to expect a British design success when the deal is announced on Monday, although any final submarine will also make heavy use of US technology. Sunak is due to travel to the west coast for a trilateral summit with Joe Biden, the US president, and Anthony Albanese, the Australian prime minister, on Monday, where he also expected to unveil a refresh of Britain’s integrated review of defence and foreign policy in the light of the war in Ukraine. Supplying Australia with a nuclear-powered submarine was the centrepiece for the Aukus defence pact, announced in September 2021, with the US and UK agreeing to share secret reactor technology in a surprise deal, so Canberra could dump an alternative diesel-powered design from France. The expectation, one source indicated, was that Australia would work jointly on a design for a next generation submarine with the UK, evolving from the existing Astute submarine design, although it may not be seaworthy until the 2040s because of the complexity of the work. Further reports last night suggested that the short-term gap could be plugged by Australia buying up to five Virginia-class submarines from the US as part of the three-way deal. Meanwhile, an alternative plan that the UK could even be willing to sell or lease the two Astute class submarines yet to be completed at Barrow, HMS Agincourt and HMS Agamemnon, is wide of the mark. Naval analysts say the UK’s submarine fleet is already stretched and could not afford a sudden reduction. Australia will become the seventh country to have a nuclear-powered submarine, relying on an enriched uranium reactor, propulsion technology that will put the country’s diesel-powered navy on a technological par with China. But it will require Australia, which is not a nuclear power, to be supplied with a reactor, a move that Beijing has argued is a breach of the Nuclear Non Proliferation Treaty. The three Aukus powers say that is not the case, and that any reactors will be supplied “welded, shielded and sealed shut” according to Australian officials overseeing the effort. The new submarines will not carry nuclear weapons. But James Acton, a nuclear expert with the Carnegie Endowment for International Peace, said it was not yet clear how the nuclear waste generated by the propulsion reactors will be dealt with – and whether that will happen in Australia or the UK or US. Defence experts said the time it would take to build the new submarines meant that there may be some related short-term developments. The US is keen to be able to base its nuclear submarines in Australia, making it easier to patrol the South Pacific, as it seeks to retain naval parity with China. A UK government spokesperson said: “When we announced the Aukus partnership in September 2021 we said there would be an 18-month scoping period to determine the optimal path to procuring Australia nuclear-powered submarines. The outcome of the scoping period is due to be announced soon.” A No 10 spokesperson said they could not pre-empt any future announcements.