Britain has sold its embassy in Thailand for a record £420 million.

The Foreign Office said it was the biggest sale in its history as well as the biggest land deal ever in Thailand.

The money will be used to modernise up to 40 Foreign Office premises around the world, including in Cairo, New Delhi and Washington.

Foreign Secretary Boris Johnson said: “Britain is a leading player on the global stage and I’m determined to ensure that our diplomats have all the necessary tools to do their job effectively.

“This includes working in modern, safe, fit-for-purpose premises not just in Bangkok, but around the world.

“Our workforce in Bangkok will be moving into a state-of-the-art premises by 2019 and this can only enhance our trade links and bilateral relations in Thailand and throughout the region.”

The site in Bangkok has been sold to a joint venture consortium of Hongkong Land, a member of the Jardine Matheson Group, and Central Group.

The Foreign Office said the existing embassy building, which dated from the 1920s, required a major upgrade to make it fit for purpose, with large parts of it no longer usable.

The new embassy building will be based in the AIA Sathorn Tower in Bangkok’s central business district.

Simon McDonald, permanent under-secretary at the Foreign Office, said: “In a tight fiscal environment, it is right that we take tough decisions to ensure that the UK can maintain a global presence while getting the best value for taxpayers.”