Labour’s plan to hand Britain’s Chagos Islands to Mauritius and then rent back a vital military base at enormous cost is facing growing resistance, not just in Westminster but across the Atlantic.
At the centre of the storm is Diego Garcia, a remote Indian Ocean atoll that hosts one of the United States’ most strategically important overseas bases.
For nearly six decades, the installation has operated under a 1966 defence treaty between London and Washington, registered with the United Nations as Treaty No. 8737, which states plainly that the territory “shall remain under United Kingdom sovereignty”.
That clause now sits uneasily alongside Labour’s proposed 2025 agreement with Mauritius, which declares that “Mauritius is sovereign over the Chagos Archipelago in its entirety, including Diego Garcia”.
The contradiction has been seized upon by Conservative peers who argue that Sir Keir Starmer’s Government is rushing headlong into a legal and diplomatic quagmire.
Lord Callanan, a former Conservative energy minister, has written formally to ministers warning that the Diego Garcia Military Base and British Indian Ocean Territory Bill appears to place Britain on course to breach its long standing defence commitments to the United States.
He highlighted that Clause 3 of the Bill would remove British sovereignty over the wider territory, leaving the UK with only limited jurisdiction over the base itself, while the old treaty with Washington still remains in force.
In carefully worded correspondence, Lord Callanan asked whether Parliament risked putting Britain in breach of international law by passing the legislation before any formal amendment to the US agreement had been secured.
Labour ministers insist there is no danger.
In her reply, Baroness Chapman, a Foreign Office minister, said negotiations with Washington were already under way and that revised arrangements would be completed before the Mauritius deal was ratified. She argued that the Bill’s key provisions would only take effect once new treaties were in place, and that Parliament was merely being asked to approve enabling legislation in advance.
But critics say this is a leap of faith on a matter of national security.
They argue that Labour is asking MPs and peers to approve the surrender of British territory first, while hoping the Americans will fall into line later. For a country that prides itself on the special relationship, that is a risky gamble.
The concern has sharpened after Donald Trump publicly attacked the handover as an “act of stupidity”, questioning why Britain would relinquish sovereignty over territory hosting a vital US base. Mr Trump, who once said the deal might “work out very well” if properly structured, has now suggested he is opposed to it.
While Washington has no formal veto over a treaty between Britain and Mauritius, the reality is more complicated. The Diego Garcia base depends on legal certainty, operational freedom and long term guarantees. If the United States were to refuse to sign a revised defence treaty under Mauritian sovereignty, Labour would face an awkward choice, pause the handover or jeopardise the very base it claims the deal is designed to protect.
That prospect explains why Conservatives have been pushing hard in Parliament to slow the legislation down.
Peers and MPs have tabled amendments demanding transparency over the true cost of the arrangement, estimated by the Government Actuary’s Department at as much as £35 billion over 99 years, and seeking stronger parliamentary oversight of the annual payments to Mauritius.
Those proposals were voted down in the Commons this week, although three Labour MPs broke ranks.
The Bill now returns to the House of Lords, where Conservative peers are preparing to renew their challenge and keep the issue in parliamentary “ping pong” for as long as possible.
Senior Conservatives say they are acting to protect British sovereignty, taxpayer money and the integrity of the country’s defence alliances.
They point out that Britain has administered the Chagos Islands for decades, maintained security, protected the surrounding waters and operated Diego Garcia in close partnership with the United States, without paying a foreign government tens of billions of pounds in rent.
Labour, by contrast, now finds itself accused of preparing to give away a strategically vital territory and then sign a near century long cheque to lease back a base Britain already controls.
With American scepticism growing, Conservative resistance hardening and legal doubts still swirling around the interaction between Britain’s old US treaty and its new Mauritian agreement, the Chagos deal is beginning to look far less settled than ministers would like to admit.
What was billed as a tidy act of decolonisation is turning into a fraught test of Labour’s judgment on sovereignty, security and Britain’s relationship with its closest ally.
And with Donald Trump openly questioning the wisdom of the handover, the Government may soon discover that giving away territory is easier on paper than it is in geopolitics.
Claire Bullivant
