Britain will reportedly spend over $47 billion, not $4.6 billion, to lease Diego Garcia under a deal returning the island territory to Mauritius

The British government will end up paying ten times more than publicly acknowledged to transfer the sovereignty of the Chagos Islands in the Indian Ocean to Mauritius, The Telegraph has reported.

The Chagos archipelago, comprising more than 60 islands, was separated from Mauritius by Britain in 1965, three years before the East African country gained independence. In 1966, the largest island, Diego Garcia, was leased to the US for military use, and around 2,000 inhabitants were displaced. Mauritius has since sought to reclaim the territory, and in 2019 the International Court of Justice advised that the UK should end its administration "as rapidly as possible."

In May, British Prime Minister Keir Starmer signed an agreement transferring sovereignty of the territory to Mauritius. The deal allows Washington and London to retain control of the joint military base on Diego Garcia for an initial period of 99 years, with a total value of $3.9 billion, according to an earlier Reuters report.

READ MORE: UK returns Indian Ocean territory to former colony

Citing documents from the Government Actuary's Department, The Telegraph said on Monday the deal will involve payments totaling nearly Pound 35 billion ($47.1 billion) over the 99-year leaseback duration, compared with the official figure of Pound 3.4 billion ($4.6 billion).

Starmer has reportedly told the House of Commons that higher estimates of Pound 9 billion ($12.1 billion) and Pound 18 billion ($24.2 billion) were "absolutely wide of the mark."

The Telegraph said the lower official total was reached by applying inflation estimates and then using an accounting method sometimes employed for long-term projects, but not typically when the government seeks to emphasize spending levels.

Conservative Party lawmakers have accused ministers of downplaying the scale of the payments, with some calling the approach "statistical jiggery-pokery" intended to mislead.

The outlet quoted a government spokesperson describing the Diego Garcia base as "essential to the security of the UK and our key allies, and to keeping British people safe." Mauritian Prime Minister Navin Ramgoolam had also previously hailed the agreement as a historic step toward "completing the total process of decolonization."