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The United Kingdom has signed a historic treaty with Mauritius, ensuring the continued operation of the UK–US military base on Diego Garcia for at least the next 99 years, in a move welcomed by its Five Eyes partners, including Australia.
The agreement cements the strategic future of one of the UK’s most critical overseas defence assets, which has supported joint UK–US operations across the Middle East, Africa, and South Asia for more than 50 years.
UK Defence Secretary John Healey MP said the treaty strengthens the UK’s alliance with the United States and reinforces national security at a time of growing global instability.
“As the world becomes more dangerous, our military base on Diego Garcia becomes more important. Today’s treaty secures full operational control, strengthens our UK–US defence partnership and keeps British people safe at home for the next 99 years and beyond,” Defence Secretary Healey said.
The base’s capabilities, including a deep-water port, airfield, GPS and satellite communications infrastructure, seismic monitoring and strategic resupply points, are seen as irreplaceable for the UK and its allies. These features support counter-terrorism, intelligence operations and power projection across critical global regions.
The deal ensures the UK retains sole operational control over Diego Garcia, including tight controls on development in nearby territories, a 24-nautical mile buffer zone and a ban on foreign forces within the archipelago. These provisions aim to prevent interference from adversaries and secure the base’s full functionality into the future.
Foreign Secretary David Lammy MP emphasised the treaty’s role in maintaining global stability, noting support from key allies including Australia, the US, Canada, and India.
“This treaty secures the Diego Garcia military base for generations to come, protecting national and global security,” Foreign Secretary Lammy said. “Doing nothing was not an option. Without this agreement, the base would have become inoperable, leaving a critical gap for adversaries to exploit.”
The UK government acknowledged that it would have likely lost any legal challenge to its continued administration of the Chagos Archipelago, following international rulings recognising Mauritian sovereignty. Without the agreement, the UK risked legally binding court orders that could have disrupted military operations and access to the base within weeks.
To avoid such outcomes, the treaty with Mauritius provides a legally binding framework that maintains UK access and operations while acknowledging the disputed sovereignty claims. The treaty also includes a commitment that no foreign security forces will be allowed on surrounding islands, effectively ruling out any third-party military presence in the region.
The deal comes at an annual cost of £101 million (AU$211 million), with a net present value of £3.4 billion (AU$7.1 billion) with details to be formally presented to the UK Parliament in the coming weeks.
Diego Garcia’s central location in the Indian Ocean places it at the heart of Indo-Pacific security, an area of growing strategic interest for Australia.
The base supports naval and air operations essential to joint defence efforts, and Australian defence officials have previously engaged in operations hosted from the island.
Its role in protecting global shipping lanes and supporting humanitarian missions has made Diego Garcia an indispensable hub for coalition forces. The agreement ensures the base’s continued role in deterring regional threats and bolstering shared intelligence and logistics networks, including through Australia’s Five Eyes alliance.
The agreement marks a rare case of the UK reaching a long-term resolution on sovereignty issues through diplomacy. While sovereignty over the Chagos Archipelago remains with Mauritius under international law, the treaty provides a framework that both secures strategic defence interests and avoids a protracted legal battle.
By reaching this agreement, the UK has avoided legal disruptions to base operations and ensured that Diego Garcia will remain a cornerstone of Western security strategy, one with lasting importance for Australia, the US and global allies alike.
