The true cost of Sir Keir Starmer’s plan to give away the Chagos Islands could be far higher than previously thought after it was revealed Britain had agreed to link payments to Mauritius with inflation.

Navin Ramgoolam, the Mauritian prime minister, said on Tuesday he had secured an inflation-linked deal from the UK that will see the cost of Britain’s lease of the Diego Garcia air base increase each year for the next century.

Sir Keir is already facing opposition from MPs and members of Donald Trump’s team over his agreement to give away the Chagos Islands.

The archipelago is claimed by Mauritius, which argues that the islands were stolen by Britain when it was given independence in 1968.

Sir Keir’s deal includes a plan for the UK to sign away the islands, but lease back Diego Garcia at a reported cost of £90 million each year for 99 years, for a total of £8.9 billion.

The Government has refused to confirm the cost of the deal, although it is understood Mauritius will be given much of the money up front.