Labour’s defence just hit a major stumbling block, writes Robert Midgley

Under the deal, Britain hands sovereignty of the islands to Mauritius and then pays to lease back Diego Garcia, the largest island.

Diego Garcia is home to a joint UK-US military base, one of the most important in the world.

Ministers repeatedly told us Britain had no choice.

They argued that the UK faced an imminent legal threat under the United Nations Convention on the Law of the Sea (UNCLOS), the international treaty that sets out the rules for the world’s oceans and territorial waters.

In May 2025, Defence Secretary John Healey told Parliament that without the agreement, the UK could face damaging legal rulings within weeks.

He said the most serious threat came from the Law of the Sea regime.

Many observers took this to mean that the outer islands, the ones without a military base, were exposed to legal action under UNCLOS.

Over time, that could put the security of the Diego Garcia base at risk.

At the heart of this is a little-known clause.

Article 298 of UNCLOS lets countries opt out of having disputes about their military activities forced before international courts.

In simple terms, it acts as a legal shield for military matters.

Critics of the deal, including former Foreign Office Special Adviser Ben Judah, argue that the Government’s case rested on the idea that this shield only covered Diego Garcia, the island with the base, and not the rest of the territory.

Now the Government’s own words have knocked that idea down.

On October 28, in a written answer to Parliamentary Question UIN 37246, Foreign Office Minister Uma Kumaran stated that the UK’s Article 298 declarations apply to “all the Overseas Territories of the UK to which UNCLOS has been extended, including … the British Indian Ocean Territory.”

Put simply, the Government has confirmed that the legal shield covers the whole of the Chagos Islands, not just Diego Garcia.

That raises an obvious question.

If the whole territory was already protected by the UK’s military exemption, why did ministers present an urgent legal threat under the Law of the Sea as a central reason for signing the deal?

It is also worth remembering that the International Tribunal for the Law of the Sea (ITLOS), the court that rules UNCLOS disputes, cannot force one country to hand its land to another.

Neither can any other international body.

The Government’s latest position is impossible to square with the urgency John Healey described when he told MPs the agreement was needed to protect the future of Diego Garcia.