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Sir Keir Starmer will next week try to sell his contentious Chagos islands deal to US President Donald Trump, amid a growing dispute over the rationale for an agreement affecting the US-UK military base at Diego Garcia.
British officials claim that criticism of the deal is based on โwild speculationโ and insist there are multiple national security grounds for striking an accord under which the UK will cede sovereignty of the Chagos Islands to Mauritius.
But the security justifications for the deal affecting the British Indian Ocean Territory (BIOT) were this week denounced in a report by the Policy Exchange, a centre-right think-tank, highlighting the risk of tense discussions when the prime minister and his team arrive in Washington.
The White House said this month it was continuing to โreview the British governmentโs agreement with Mauritius and the potential implications for the Naval Support Facility Diego Garciaโ.
Jim Risch, Republican chair of the Senateโs foreign relations committee and a Trump ally, told Policy Exchange this week that the deal represented a โdangerous surrenderโ to Beijing as it would allow Chinese influence to grow in the region.
Jonathan Powell, Starmerโs national security adviser, held talks this month with his US counterpart Mike Waltz on the Chagos deal, and Starmerโs allies said they expect the prime minister to discuss the issue with Trump.
Ahead of the visit, British officials claimed that the deal between the UK and Mauritius, which would involve the UK leasing Diego Garcia for a 99-year period, would put the base on a โsecure footingโ.
Britain has argued that international legal rulings on the status of the archipelago cast doubt over the future operation of the air base and port facility on Diego Garcia.
Downing Street said: โThe legal and security advice is very clear that the operation of the base will be at risk if there is not a deal.โ Under the plan, Britain is giving up sovereignty over the Chagos to Mauritius.
British officials said people had become โfixatedโ on an International Court of Justice ruling in 2019 which said Britainโs sovereignty over the islands should end as quickly as possible.
They added that other problems could arise, including the possibility that some countries could refuse to allow โoverflightโ rights for aircraft supplying the strategically important UK-US base in the Indian Ocean.
A spokesperson for Starmer has also claimed that โthe electromagnetic spectrum at the Diego Garcia base would not be able to continue to operate without a dealโ, potentially threatening secure communications.
โItโs something that the UK and the US have currently got unique access to, and it is the case that without legal certainty over the base [it] is something we would lose access to,โ the spokesperson added.
Both claims were rejected in a Policy Exchange report which said that even chartered civilian planes flying to Diego Garcia were not within the purview of the International Civil Aviation Organization, a UN agency, as long as they were used for a military purpose.
โFlights to and from the base are excluded from the scope of the ICAOโs purview, as the organisation only deals with civilian aviation,โ the report said.
The report claimed that Downing Streetโs concern about secure communications had โno basis in realityโ and that they could not be affected by rulings by the International Telecommunication Union, another UN agency.
โThe ITU simply does not have the power to prevent the UK and the US from using the radio spectrum associated with the BIOT, and it does not have mechanisms to enforce its decisions,โ it said.
Tom Tugendhat, former Conservative security minister, said: โIt is past time for the government to come to its senses, to remember its duty to defend the UKโs vital strategic interests, andย to walk away from the deal.โ
