Stephen Doughty, a foreign office minister, told parliament that reports in the British media that the cost of payments to retain the base could rise from £9 billion to £18 billion were “categorically untrue”.

“There is no change to the substance or the quantum in relation to the agreement,” he said.

“There is a huge amount of speculation, I would take the vast majority of it with a pinch of salt.”

Britain struck a deal in October to cede sovereignty of the Chagos Islands to Mauritius – a former colony that became independent in 1968 – while retaining control under a 99-year lease of the military base on Diego Garcia, the largest island of the Chagos archipelago.

However, the Mauritian Prime Minister Navin Ramgoolam, who was elected in November, has questioned the deal, and US President Donald Trump’s team are also examining the agreement.

Ramgoolam said yesterday that Britain had agreed to a number of changes, including that the lease could only be extended with the agreement of both countries.

He also added that payments for the lease would be front-loaded and protected from inflation, which could increase the cost in real terms.

The British government has so far refused to reveal details of the cost of the deal.

Priti Patel, the spokesman on foreign affairs for the opposition Conservative Party, told parliament the deal was “one of the worst foreign policy failures in modern British history”.

“Labour are surrendering an absolutely critical, strategic defence asset,” she said. ”

And now we are told that we have to pay billions for privilege of doing so.”

A non-binding resolution in the United Nations General Assembly in 2019 said Britain should give up control of the archipelago after wrongfully forcing the population to leave.