Rishi Sunak will fly to San Diego on Sunday to unveil plans to provide Australia with nuclear-powered submarines under the Aukus plan amid concerns over 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 over Beijing’s economic coercion and foreign policy goals, Britain’s defense and security strategy for the 2020s is being updated, with the revised version due to be published on Monday.

It will address “increasingly worrying behaviour” from Chinese President Xi Jinping’s government, the “serious risks” posed by Russia following a renewed attack 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 Britain, the US and Australia in September 2021 – as “our greatest source of strength and security”.

He added: “I am traveling to the US today to launch the next stage of the Aucus nuclear submarine program, a project that binds our closest allies and delivers security, new technology and economic benefits at home.”

Britain would be “safe, prosperous and standing shoulder to shoulder with our partners”, thanks to the program and the updated Integrated Review, Sunak said.

He will hold meetings on Sunday night and Monday, before flying home ahead of the Budget on Wednesday.

The visit threatened to overshadow Sunak’s trip to Paris on Friday, given the French government’s reaction to the scrapping of its own submarine deal with Australia a year and a half ago.

Britain is stepping up efforts to increase its influence in the Indo-Pacific region, and Sunak hopes Monday’s trilateral summit will demonstrate his commitment to standing up to Chinawhich senior Conservative MPs have urged him to take a tougher line on.

The Guardian was revealed earlier this week that Sunak had expressed delight to other ministers at the outcome of the negotiations, with several sources saying they believed the eight nuclear-powered submarines would be based on British designs.

Such a move would secure the long-term future of the shipyard in Barrow-in-Furness, as the entire fleet may not be seaworthy until the 2040s.

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Reports this week suggested the short-term gap could be closed by Australia buying up to five Virginia-class submarines from the US.

Under the three-way agreement, the US and UK will agree to share secret reactor technology.

Australia will become the seventh country to have a nuclear-powered submarine, which relies on an enriched uranium reactor – putting its diesel-powered fleet on a technological level with China.

But that will require Australia, which is not a nuclear power, to be fitted with a reactor, a move Beijing has argued is a violation of the Nuclear Non-Proliferation Treaty.

The three Aukus powers say that is not the case, and that all reactors will be delivered “welded, shielded and sealed closed,” according to Australian officials overseeing the effort.

Charles Edel, senior adviser at the think tank Center for Strategic and International Studies, has described the Aukus Pact as a calculated gamble.

“It is a bet that by further integrating industrial capabilities and increasing interoperability, it will significantly increase the capabilities of our allies, make them more powerful and ultimately change Beijing’s calculations about its security environment,” he said.

“And that in doing so, it will help stabilize a region badly destabilized by China’s rapid expansion of military capabilities and increasingly aggressive foreign policy.”