The HMS Queen Elizabeth passed through Asia in 2021, making port calls in Japan, as Western allies push back against China's growing military power in the region.

Sunak, who is in Japan for the G7 summit in Hiroshima, stopped first in Tokyo to visit a naval base, where he announced Britain will double the number of UK troops in upcoming joint exercises.

London and Tokyo will also agree a formal "consult clause", committing them to discuss regional and global security issues and measures in response.

Sunak said the returning Carrier Strike Group would "work alongside the Japanese Self Defense Forces and other regional partners to help defend peace and stability in the Indo-Pacific".

He will meet later Thursday in Hiroshima with Japanese Prime Minister Fumio Kishida, with the pair expected to announce the "Hiroshima Accord".

The agreement will cover deals on defence, trade, science and technology, and issues like climate change, Downing Street said, without giving further details.

Before his departure for Japan, Sunak said the summit was coming "at a pivotal moment" for the alliance as it faces "complex threats to global peace and prosperity".

He said Britain would "galvanise international action on economic coercion by hostile states and shore up support for Ukraine".

Sunak, who became premier in October, departed Britain under growing domestic political pressure following disastrous local election results earlier this month that saw his Conservative party routed.

Meanwhile, the worst cost-of-living crisis in a generation shows little sign of abating, with inflation remaining stubbornly high and fuelling industrial action as workers demand pay increases to match rising prices.