The dismissal of Lord Mandelson from his Washington role has immediate implications for the controversial Chagos sovereignty negotiations.
Mandelson was not a peripheral figure. According to US sources, he played a central role in persuading the Trump administration to accept the so-called “Chagos Surrender Deal” that Keir Starmer was determined to see through.
Multiple officials in Washington confirm that many within the administration were unaware of the UK proposal until Mandelson arrived in post. From that point, he pursued an intensive lobbying effort, described by one source as “night and day”, to secure American acquiescence. The motivation was clear: Starmer feared that a flat rejection in the Oval Office would expose the weakness of his policy. Mandelson and Foreign Secretary David Lammy worked closely to “lubricate” US officials and minimise congressional opposition.
In London, Mandelson’s intervention was regarded as a test case for his influence in Washington and his proximity to Trump. He privately boasted that his work had won critical US backing for the agreement. But with Mandelson now disgraced and removed from the field, those assurances are suddenly in question.
With a new ambassador in post, one not so closely tied to Starmer, the US administration has a fresh opportunity to revisit the matter. That prospect has gained urgency this week following a letter sent to President Trump by the Great British PAC, signed by more than 40 senior British figures including former Cabinet ministers, defence secretaries, and security experts.
The letter is unequivocal. It warns that transferring sovereignty over the Chagos Archipelago to Mauritius would amount to “a deliberate act of strategic self-harm that threatens both British and American security.”
Their reasoning is straightforward:
- Diego Garcia, the key US base in the Indian Ocean, would fall under the sovereignty of a state bound by the Pelindaba Treaty, Africa’s nuclear-weapon-free zone agreement. Mauritius is a party; the US is not.
- This would introduce legal ambiguity around the basing of nuclear-capable forces, inviting adversaries such as China and Russia to exploit treaty provisions to constrain American operations.
- Mauritian “assurances” cannot be relied upon. Under Chinese influence, or amid UN/IAEA agitation, Port Louis could be pressured into inspections, disputes, or denunciations of US deployments.
- Diego Garcia has never been under Mauritian administration. This is not restitution; it is the voluntary abandonment of a British Overseas Territory that anchors Western security.
The signatories conclude that, if the UK and US were prohibited from storing or transferring nuclear weapons through Diego Garcia, the consequences for deterrence and power projection would be severe. They call on Trump to oppose the surrender and to ensure that Diego Garcia remains exempt from Pelindaba Treaty constraints.
With Mandelson’s departure, the political equation has shifted. The “safeguards” he claimed to have secured for Starmer were dependent on his personal lobbying and connections. Those guarantees have evaporated. What remains is a deeply flawed proposal that Parliament, Congress, and the US administration must scrutinise afresh.
The Chagos file should be reopened in Washington. The costs of inattention are simply too high.
