LONDON — Britain must address the potential threat from China when its Indian Ocean deal with Mauritius regarding the Chagos group of islands expires, senior British lawmakers have warned Foreign Secretary David Lammy.

“Renewal provisions” in the £3.4 billion deal relinquishing sovereignty over the Chagos Archipelago to Mauritius “are a potential source of future vulnerability in the face of growing military ambitions by China” in the area, Rupert de Mauley, chair of the House of Lords International Relations and Defence Committee, said in a letter to Lammy, on behalf of the committee.

Under the controversial Chagos agreement, struck in May, Britain will retain control of a U.K.-U.S. military base on Diego Garcia — the largest of the Chagos islands — on a 99-year lease.

The decision to hand over the Chagos Islands came after a non-binding ruling from the International Court of Justice pressured the U.K. to allow Chagossians — who were removed between 1968 and 1973 to make way for the Diego Garcia base — to return, ending years of legal uncertainty.

But conservative critics of the Chagos deal in the U.K. have argued it hands control of the strategically vital territory to a country with links to China, and represents poor value for British taxpayer money.

De Mauley’s committee launched a brief probe into the implications of the transfer shortly after the deal was struck. 

“Things can change significantly over a span of 99 years, including in ways that cannot be predicted,” said an annex to de Mauley’s letter to Lammy, published Thursday. “While the Agreement can be renewed for a further 40 years after the initial 99-year term — and for a further period subsequently — we heard that there was ‘no assurance of renewal’ and that this would depend on the goodwill of future Mauritian governments (and UK intentions).”

While his committee had been “assured that the Agreement safeguards current operational freedoms,” de Mauley added in comments to POLITICO that it was “imperative that the Government remain vigilant and proactive in addressing potential future vulnerabilities, given China’s growing military ambitions in the Indian Ocean.”  

De Mauley also warned that “public messaging on the strategic benefits of the base” would be critical. Given the costs involved in leasing the base, he added, the government should be “alert to attempts by hostile powers that may wish to leverage this to erode public support for the U.K.’s presence on Diego Garcia.”