More than 40 former ministers, members of Parliament, peers and national security figures have written to US President Donald Trump urging him to oppose a UK plan to transfer sovereignty of the British Indian Ocean Territory (BIOT) to Mauritius, saying the move would harm Anglo-American security and could be far more costly than London has acknowledged.
The letter, circulated ahead of Mr Trump’s state visit to Britain and his planned talks with Prime Minister Sir Keir Starmer, was signed by former Conservative leader Sir Iain Duncan Smith, ex-defence secretary Sir Grant Shapps and former home secretary Suella Braverman, among others. It was also backed by a Labour MP, peers, military veterans, legal experts and national security professionals.
The correspondents said the planned handover, agreed between the UK and Mauritius earlier this year after a prolonged legal dispute, would place Diego Garcia — home to a long-standing US military presence — under the jurisdiction of a state party to the Pelindaba Treaty, Africa’s nuclear-weapon-free zone. The letter warned that could create "dangerous legal ambiguity" over US nuclear-capable operations and expose the base to inspections, legal challenges or operational restrictions that would "erode US deterrence and diminish Western security." The authors described the deal as a "deliberate act of strategic self-harm."
Downing Street has said the UK will transfer sovereignty by the end of the year and immediately enter a 99-year leaseback for the military base on Diego Garcia. The government has estimated the financial settlement at £3.4 billion. The TaxPayers’ Alliance, however, has suggested the cost could reach as much as £47 billion if market predictions of higher inflation are applied to the deal’s terms.
According to No. 10, Mr Trump gave an informal indication of support for the Chagos agreement in February and had "signed off" on the deal before it was formally agreed, telling Sir Keir that he was "inclined to go with your country" and that he had "a feeling it’s going to work out very well." The letter’s signatories appealed directly to Mr Trump to use his influence "publicly and privately, and your prerogatives under the US-UK defence agreement of 1966 to oppose this surrender."
The UK government has scheduled a second reading of the Chagos Bill this week in Parliament. Campaigners and some legal observers have said the transfer followed decades of litigation and contested legal rulings, and the move remains subject to further legal challenge. A judicial review relating to the deal is due in November.
Mauritius has long asserted sovereignty over the BIOT, a position supported by some international legal opinions and diplomatic pressure. The UK has maintained administrative control of the islands since the 1960s while allowing the US to operate a strategic base on Diego Garcia. Critics of the current agreement argue that the combination of a sovereign transfer and a leaseback does not sufficiently insulate the military arrangements from future legal or political interference.
Supporters of the agreement within government have framed it as a resolution of a protracted dispute and a means of preserving the operational status of the base through the long leaseback. Opponents contend the terms leave key risks unaddressed and seek international reassurance that defence arrangements will remain unaffected. The exchange of letters and the timing of Mr Trump’s visit underscore the diplomatic sensitivity of the issue as lawmakers and former officials press both governments for clarity on security guarantees and the financial implications of the settlement.