Rishi Sunak will fly to San Diego on Sunday to unveil plans for supplying Australia with nuclear-powered submarines under the Aukus scheme amid concerns about the growing threat from China. A major announcement 18 months in the making is expected when the UK prime minister meets his Australian counterpart, Anthony Albanese, and US president Joe Biden. In response to concerns about Beijing’s economic coercion and foreign policy aims, the UK’s defence and security strategy for the 2020s is being updated, and the revised version is due to be published on Monday. It will address “increasingly concerning behaviour” by Chinese president Xi Jinping’s government, the “grave risks” posed by Russia after a renewed assault on Ukraine and “hybrid threats” to Britain’s economy and energy security, No 10 said. Before his trip to California, Sunak hailed “global alliances” – such as the one formed between the UK, US and Australia in September 2021 – as “our greatest source of strength and security”. He added: “I am travelling to the US today to launch the next stage of the Aukus nuclear submarine programme, a project which is binding ties to our closest allies and delivering security, new technology and economic advantage at home.” The UK would be “secure, prosperous and standing shoulder-to-shoulder with our partners”, thanks to the programme and the updated Integrated Review, Sunak said. He will hold meetings on Sunday night and Monday, before flying back home before the budget on Wednesday. The visit threatened to cast a shadow over Sunak’s trip on Friday to Paris, given the French government reacted with consternation to its own submarine deal with Australia being scrapped a year and a half ago. Britain is stepping up efforts to increase its influence in the Indo-Pacific, and Sunak hopes the trilateral summit on Monday will demonstrate his commitment to standing up to China, which senior Conservative MPs have urged him to take a tougher stance on. The Guardian revealed earlier this week that Sunak had expressed delight to fellow ministers about the outcome of negotiations, with multiple sources saying they believed the eight nuclear-powered submarines would be based on British designs. Such a move would safeguard the long-term future of the shipyard at Barrow-in-Furness, since the full fleet may not be seaworthy until the 2040s. Reports this week suggested that the short-term gap could be plugged by Australia buying up to five Virginia-class submarines from the US. Under the three-way deal the US and UK will agree to share secret reactor technology. Australia will become the seventh country to have a nuclear-powered submarine, relying on an enriched uranium reactor – putting its 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. Charles Edel, a senior adviser at the Center for Strategic and International Studies thinktank, has described the Aukus pact as a calculated gamble. “It’s a bet that by further integrating industrial capacities and increasing interoperability it will significantly augment the capabilities of our allies, make them more powerful, and ultimately change Beijing’s calculations about its security environment,” he said. “And that by doing so, it will help stabilise a region that has been badly destabilised by China’s rapid expansion of military capabilities and increasingly aggressive foreign policy.”