UK secures future of vital Diego Garcia Military Base to protect national security

The UK has today (22 May) signed a landmark agreement with Mauritius to secure the future of the strategically critical UK-US military base on Diego Garcia, one of our most significant contributions to the transatlantic defence and security partnership.

The base has played a vital role in defending the UK and its allies for over 50 years. This new deal ensures its continued operation for at least the next century, protecting capabilities essential to UK intelligence and counter-terrorism.

The base plays a key role in operations that support UK forces and our allies across the Middle East, East Africa and South Asia.

Its deep-water port, airfield, and advanced communications and surveillance capabilities give the UK and its allies crucial strategic capabilities, which have played a key role in missions to disrupt high-value terrorists, including Islamic State threats to the UK.

The legal necessity of this deal has been recognised by successive governments. The previous government started these negotiations over two years ago, and they held 11 out of the 13 rounds of talks that underpin the deal, that this government has concluded.

Crucially, all Five Eyes partners – the US, Canada, Australia, and New Zealand – back the agreement, along with India, recognising the critical role Diego Garcia plays in upholding global stability and deterring adversaries.

The base is a cornerstone of the Government’s Plan for Change, with operations there deterring threats to our nation and protecting our economic security.

Defence Secretary, John Healey MP said 

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. 

Without this base, our ability to deter terrorists, defend our interests and protect our troops around the world would be at risk. This agreement will safeguard our national and economic security for generations to come. 

Critically, the deal ensures the UK retains full operational control of Diego Garcia, including management of the electromagnetic spectrum satellite used for communications – vital for countering hostile interference.

There will also be robust provisions to keep adversaries out, including

• A 24 nautical mile buffer zone where nothing can be built or placed without UK consent – meaning we can protect UK interests.

• A rigorous process, including joint decision-making, to prevent any activities on the wider islands – some over 100 nautical miles away – from disrupting base operations. Joint decision-making means there can be no development unless we agree. 

• A strict ban on foreign security forces on the outer islands, whether civilian or military.

• A binding obligation to ensure the base is never undermined.

Both countries have also agreed to a ban on the presence of foreign forces across the wider territory and a binding guarantee that base operations cannot be undermined.

Without this deal, international legal proceedings could have rendered the base inoperable, affecting UK national security in the process with our adversaries being allowed to capitalise on this – building outposts near the base.

Within a matter of weeks, with no deal, the UK could face legally-binding provisional measures through an Arbitral Tribunal under the Law of the Sea Convention – affecting the ability of the Armed Forces to patrol the waters around the base.

Foreign Secretary David Lammy MP said 

This treaty secures the Diego Garcia military base for generations to come, protecting national and global security. 

Without this deal, the land, sea and air operations of the base would become inoperable – doing nothing was not an option. 

The US, Australia, Canada and India all back this deal because they understand its importance for global security. This government has always been clear that we will act in the national interest, not gamble with our national security like those who oppose this deal.

It was clear that this agreement was the only route to securing the future of the base and preventing the UK’s adversaries from establishing a presence in the region.

It is a clear demonstration of the UK’s commitment to act decisively in defence of its interests and ensure that the base continues to support operations that keep British citizens safe, now and in the decades to come.

Notes to editors

• The cost per year is £101 million and the net present value of payments under the treaty is £3.4 billion. All costs have been verified by the Government Actuary’s Department. 
• Further details will be laid out in Parliament.

Diego Garcia Capabilities

Diego Garcia is the largest island of the Chagos Archipelago, located in the central Indian Ocean. The joint UK-US military base on Diego Garcia has a strategic location which makes it vital to UK and US power projection in the Indian Ocean and beyond. The base provides a unique shared platform with irreplaceable security capabilities that enable a UK and US military presence across the Middle East, Indo-Pacific and Africa.

Strategic and operational importance

• Diego Garcia’s strategic location allows it to support a wide array of operational activity in a number of theatres, helping to combat some of the most challenging threats, including terrorism, and hostile states.
• Diego Garcia is the only UK base in the region with guaranteed freedom of use. It is central to current UK and US emergency planning and operations, just as it was with Afghanistan and Iraq.
• The base offers the UK and its Allies unique and vital capabilities that help us understand and anticipate those who would do us harm. This includes capabilities which have been used to support counter terrorism operations against high value Islamic State targets. 
• The base is a critical logistics hub at a strategic location, with a full range of facilities that acts as a key refuelling and resupply station for naval and air operations. This enables power projection and global reach, allowing for rapid and flexible deployment of our forces across the Middle East, East Africa and South Asia.
• The base helps protect some of the most important shipping lanes in the world, while also remaining isolated enough to be protected from attack by adversaries.
• The close collaboration between UK and US delivers shared real-world operational outcomes, in the Indo-Pacific, Africa, and the Middle East. The base has also hosted visits from Allies and partners such as Japan, France, Republic of Korea and Australia.

Base capabilities

• Airfield Location and infrastructure accommodate a broad range of military aircraft, with capability to support military requirements from strike operations, as seen through the Afghanistan and Iraq campaigns, to humanitarian response.
• Port A multitude of berthing options for the UK and US navies to support various missions including Carrier Strike Group deployment. The UK maintains a Nuclear Emergency Response Organisation to permit nuclear powered submarines to safely berth at the port. The US uses Diego Garcia to strategically position equipment and supplies at sea for rapid deployment in various global theatres, including for humanitarian aid and disaster relief missions over the years, across the Indo-Pacific.
• Seismic monitoring Permanent location of three pieces of critical Comprehensive Nuclear Test Ban Treaty monitoring equipment, a network constantly monitoring for indicators of nuclear testing, vital in preventing nuclear proliferation.
• Space capabilities Hosts one of the monitoring stations and one of the four ground antennas for the Global Positioning System (GPS). Also hosts part of the Ground-Base Electro-Optical Deep Space Surveillance (GEODSS) System. This provides situational awareness of objects in Earth’s orbit, helping to track space debris that pose a risk to space systems.

Government Legal Position – Diego Garcia

Mauritius’s legal claim of sovereignty over the island of Diego Garcia is supported by a number of international institutions, including the UN General Assembly.

The International Court of Justice considered this issue in an Advisory Opinion delivered on 25 February 2019. An Advisory Opinion of the ICJ carries significant weight; in particular it is likely to be highly influential on any subsequent court/tribunal considering the issues arising out of disputed sovereignty, and whose judgment would be binding in international law. The ICJ concluded that “the United Kingdom is under an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible”.

The 2019 Advisory Opinion was followed in 2021 by a Special Chamber of the International Tribunal for the Law of the Sea (in a case about delimitation of the boundary between Mauritius and The Maldives) which ruled that Mauritius’ sovereignty was inferred from the ICJ’s determinations.

If a long-term deal is not reached between the UK and Mauritius, it is highly likely that further wide-ranging litigation would be brought quickly by Mauritius against the UK. This might, for example, include further arbitral proceedings against the UK under Annex VII of the UN Convention on the Law of the Sea (“UNCLOS”). A judgment from such a tribunal would be legally binding on the UK.

The longstanding legal view of the United Kingdom is that the UK would not have a realistic prospect of successfully defending its legal position on sovereignty in such litigation. Even if the United Kingdom chose to ignore binding judgments made against it, their legal effect on third countries and international organisations would give rise to real impacts to the operation of the Base and the delivery of all its national security functions. International organisations have already adopted decisions based on Mauritian Sovereignty, and others would follow suit following such litigation.  

These impacts could include our ability to protect the electromagnetic spectrum from interference, to ensure access to the Base by air and by sea, effectively to patrol the maritime area around the Base, and to support the Base’s critical national security functions.

Further, the UK would likely face a Provisional Measures Order within a matter of weeks of Mauritius commencing proceedings, which would also be legally binding. That would mean facing the sorts of detrimental impacts set out above, with the effect of substantially disrupting the operation of the military Base, in very short order.

This deal is thus the only way to secure unfettered access to the Base for the long-term and to ensure its full contribution to national security.