People in London were treated to an RAF display earlier as military jets flew over the capital.
A Voyager and two Typhoons zoomed through the skies of London at around 11am to mark the visit of Japan prime minister Fumio Kishida.
It was his first official visit to the UK.
UK prime minister Boris Johnson and Mr Kishida watched the RAF flypast together in Horse Guards Parade before their bilateral discussions in Downing Street.
The two leaders headed then headed to No 10 afterwards to discuss a new defence deal.
No 10 said the "landmark" reciprocal access agreement would allow the two countries' forces to deploy together for training, joint exercises and disaster relief.
Downing Street said the leaders were expected to agree in principle a “landmark” reciprocal access agreement (RAA), which would allow Japanese and British forces to deploy together to carry out training, joint exercises and disaster relief activities.
Mr Johnson said: “As two great island democracies, and the third and fifth largest economies in the world, the UK and Japan are focused on driving growth, creating highly skilled jobs and ensuring we remain technology superpowers.
“The visit of prime minister Kishida will accelerate our close defence relationship and build on our trade partnership to boost major infrastructure projects across the country – supporting our levelling up agenda.”
Downing Street added the agreement would boost the UK’s commitment to the Indo-Pacific and further safeguard global peace and security, and build on the already close collaboration on defence and security technology between both nations.
It follows the government’s defence and foreign policy integrated review, published last year, which announced a “tilt” towards the Indo-Pacific.
In September, Australia, the UK and the US signed up to the Aukus pact to develop nuclear-powered submarines for Canberra in a bid to increase joint naval activity in the region.
The government describes Japan as its closest security partner in Asia.
It says the island nation only has two other bilateral visiting forces agreements, one with the United States and the recently agreed RAA signed with Australia in January.
The two G7 leaders are also expected to discuss Russia’s illegal invasion of Ukraine and how to exert pressure on President Vladimir Putin’s regime.
