Rishi Sunak will unveil a new agreement with Japan to foster closer defence, security and cyber ties amid growing concerns about the threat from China.
Visiting Tokyo, the Prime Minister will commit to deploying a naval battle fleet in the Indo-Pacific in 2025 and to double UK troop numbers in upcoming joint exercises.
He will agree to launch a partnership on semiconductors in order to reduce the reliance on Beijing for the supply of the essential microchips before attending the G7 summit.
The “Hiroshima Accord” will be formally agreed on Thursday between Mr Sunak and his Japanese counterpart Fumio Kishida ahead of the meeting of world leaders in the city hit by the atom bomb.
But he will not hold more personal bilateral talks with the US president, instead sitting down with Mr Kishida, France’s Emmanuel Macron and India’s Narendra Modi.
Mr Sunak will be joined by his wife Akshata Murty, as she joins the G7’s “partners’ programme” in her first official foreign visit since they entered No 10.
Under the agreement with Japan, Mr Sunak will commit to deploy the Navy’s carrier Strike Group to the Indo-Pacific in 2025.
Including an aircraft carrier and fighter jets, the fleet will work with the Japanese military and other allies to defend peace and stability in the region.
A fourth UK-Japan “vigilant isles” military exercise taking place in Japan later this year is being billed as the biggest yet and will include around 170 UK service personnel.
The UK and Japan are also expected to commit to consulting each other on key regional and global security issues and to consider measures in response.
They will also launch the semiconductors partnership to make use of British expertise and Japan’s materials to bolster supply chains amid concerns over Chinese dominance.
On the plane to Tokyo, Mr Sunak told reporters one of his priorities for the summit was ensuring “we as G7 allies are aligned in our approach to protecting ourselves against the risks and challenges that China poses”.
In a statement, the Prime Minister said: “It is a privilege to be visiting Tokyo and Hiroshima at this historic moment in the United Kingdom’s relationship with Japan.
“Prime Minister Kishida and I are closely aligned on the importance of protecting peace and security in the Indo-Pacific and defending our values, including free and fair trade.
“The Hiroshima Accord will see us step up co-operation between our armed forces, grow our economies together and develop our world-leading science and technology expertise.
“It marks an exciting next phase in the UK and Japan’s flourishing partnership.”
The trip takes place as Mr Sunak grapples with Tory infighting heightened by the party’s large-scale losses in the local elections.
At the G7 summit starting on Friday, Mr Sunak will discuss shoring up support and holding Vladimir Putin’s Russia to account among his priorities.
The Prime Minister will reflect on the “sombre reminder of the human cost of all-out war” while visiting Hiroshima, where he will plant a tree to remember victims of the atom bomb.
Mr Sunak’s official spokesman said: “The visit is a crucial opportunity to build our relationship with Japan, already one of the UK’s strongest and most important partners.
“The summit is an opportunity for the G7 to demonstrate unified resolve and action in the face of threats from autocratic states – threats to global prosperity, security and sovereignty.”