Labour’s plan to hand Britain’s Chagos Islands to Mauritius and then rent back a vital military base at vast cost is facing renewed pressure after a senior Conservative peer escalated warnings that the Government risks breaching international law unless it secures United States consent first.
At the centre of the row is Diego Garcia, a remote Indian Ocean atoll that hosts one of Washington’s most strategically important overseas installations.
For nearly six decades the base 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 sits awkwardly beside Labour’s proposed 2025 agreement with Mauritius, which declares that “Mauritius is sovereign over the Chagos Archipelago in its entirety, including Diego Garcia”.
Conservative peers have seized on the contradiction, warning that Parliament is being asked to legislate for the surrender of British territory before Britain’s existing defence commitments to the United States have been properly rewritten.
Lord Callanan, a former Conservative Cabinet minister, has now written again to Foreign Office ministers pressing them on the timing and legality of any new arrangement with Washington.
In his latest letter he notes that ministers themselves have acknowledged the 1966 treaty “would no longer reflect the status of Diego Garcia” if the Mauritius deal were ratified. That, he argues, makes it essential that amendments to the American treaty are concluded first, otherwise Britain would be left in breach of international law.
Lord Callanan also invoked the Constitutional Reform and Governance Act, which requires any treaty, or any amendment to an existing treaty, to be laid before Parliament for scrutiny for at least twenty one sitting days before ratification.
He demanded confirmation that any revised agreement with the United States would be subjected to that process, and that it would be improper for Labour to push ahead with the Diego Garcia Bill or ratify the Mauritius treaty until Parliament had approved the American changes.
The intervention intensifies Conservative claims that Labour is attempting to rush through legislation while key international negotiations remain unresolved.
Earlier, Baroness Chapman, a Foreign Office minister, had insisted that talks with Washington were well advanced and that a new UK US agreement would be finalised before the Mauritius treaty came into force. She argued that the Bill’s operative clauses would only be triggered once new international arrangements were in place.
But critics say Lord Callanan’s follow up exposes how much still rests on assumption rather than certainty.
They argue that Labour is asking MPs and peers to sign off the surrender of British sovereignty now, while trusting that the White House will later accept a radically altered legal framework for a base it has relied on since the Cold War.
That gamble looks increasingly fraught after Donald Trump publicly attacked the proposed handover as an “act of stupidity”, questioning why Britain would relinquish territory hosting a vital US facility. Although he once suggested the deal might “work out very well” if properly structured, the former president has since indicated he opposes it outright.
While Washington has no formal veto over a treaty between Britain and Mauritius, the practical reality is more complicated. The Diego Garcia base depends on legal certainty, operational freedom, and long term guarantees. If the United States declined to sign a revised treaty placing the installation on Mauritian sovereign territory, Labour would face a stark choice, pause the handover, or risk undermining the very base ministers say the deal is designed to protect.
That prospect explains why Conservatives have intensified their parliamentary campaign.
Peers and MPs have tabled amendments demanding transparency over the true cost of the arrangement, estimated by the Government Actuary’s Department at up to thirty five billion pounds over ninety nine years, and seeking Commons approval of the annual payments to Mauritius.
Those proposals were voted down this week, although three Labour MPs broke ranks.
The Bill now returns to the House of Lords, where Conservative and cross bench peers are preparing to prolong the legislative battle in what Westminster calls “ping pong”, sending amendments back to the Commons repeatedly in an effort to force concessions.
Senior Conservatives say they are acting to defend British sovereignty, taxpayers’ money, and the integrity of Britain’s defence alliances.
They point out that Britain has administered the Chagos Islands for decades, maintained security in surrounding waters, protected the archipelago’s environment, 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, is accused of preparing to give away a strategically vital territory and then writing a near century long cheque to lease back a base Britain already controls.
With American scepticism growing, Conservative resistance hardening, and unresolved legal questions hanging over the relationship between Britain’s old US treaty and its proposed Mauritian settlement, the Chagos deal is beginning to look far less settled than ministers would like to suggest.
What was billed as a tidy act of decolonisation is fast becoming a searching test of Labour’s judgment on sovereignty, security, parliamentary accountability, and Britain’s most important alliance.
And as Lord Callanan’s latest intervention underlines, the battle is no longer only about the future of distant islands in the Indian Ocean, but about whether Parliament is being asked to sign away British territory before the legal ground beneath Britain’s closest military partnership has even been secured.
Claire Bullivant
Image: Lord Callanan. Credit: UK Parliament Attribution 3.0 Unported (CC BY 3.0) licence.
