Main points
After entry into force of the UK-Mauritius Agreement on the Chagos Islands, including Diego Garcia:
- there will be no change to the British nationality status that any Chagossian currently holds
- there will be no changes to current Chagossian rights to acquire British Citizenship
- there will be changes to the rights of Chagossians to claim British Overseas Territories Citizenship status through a connection to the British Indian Ocean Territory (BIOT). These changes will only come into force when the necessary primary and secondary legislation is in place
Diego Garcia treaty
On 22 May 2025, the UK and Mauritian Governments signed a landmark agreement to secure the future of the strategically critical UK-US military base on Diego Garcia.
After entry into force of the Treaty, Mauritius will be sovereign over the Chagos Archipelago, including Diego Garcia. As a result of the Treaty, the British Indian Ocean Territory (BIOT) will no longer be a British Overseas Territory.
UK law
Before the treaty can come into force, changes to UK law are required. The UK government will make these changes through the Diego Garcia Military Base and British Indian Ocean Territory Bill, which was introduced to Parliament on 15 July 2025.
The Bill includes a provision to update the British Nationality Act 1981 to reflect that the BIOT will no longer be a British Overseas Territory.
British citizenship
The changes made to the British Nationality Act will maintain Chagossian rights to claim British citizenship under the route set up in 2022.
There will be no changes to the citizenship that anyone currently holds, nor to the rights of Chagossians to claim British citizenship under current routes.
British Overseas Territories Citizenship (BOTC)
On entry into force of the Treaty, BIOT will cease to be an Overseas Territory (OT). Once it ceases to be an OT, the right to claim British Overseas Territories Citizenship based on a connection to BIOT will lapse.
This means that, after the treaty enters into force, Chagossians will not be able to apply for British Overseas Territories Citizenship under the route set up in 2022. Those who currently hold British Overseas Territories Citizenship through their connection to BIOT will not be able to pass it down to descendants born after the treaty enters into force.
If any Chagossian who has claimed British Overseas Territories Citizenship has a child born before entry into force, that child will only be able to claim British Overseas Territories Citizenship if they make an application under the 2022 route, before entry into force.
If any member of the Chagossian community does not already have British Overseas Territories Citizenship and would like to claim it based on their connection to BIOT, they will be able to do that through the 2022 route until entry into force of the Treaty.
Being unable to claim British Overseas Territories Citizenship will not affect Chagossians’ continuing right to claim British Citizenship under the 2022 route for Chagossians, until expiry of that route.
Frequently asked questions and answers
Q. How will these changes impact Chagossians’ current citizenship status?
- these changes will not affect the current citizenship status of any Chagossian
Q. Will there be changes to the deadline Chagossians currently have to apply for British citizenship?
Q. How do I know if I already hold British Overseas Territory Citizen (BOTC) status or need to apply?
Q. Can my children become BOTC?
- your children’s nationality status will not change
- if your child was born before you attended a citizenship ceremony, they can make an application under the 2022 route to become a British citizen. If they do so before entry into force, they will also become a BOTC
- any children born after the treaty comes into force will not be able to acquire BOTC through a connection to BIOT but remain eligible to apply for British citizenship, if they are not already a British citizen
