The Tory leader says Labour's negotiations could cost the UK billions; the prime minister questions whether Badenoch has been "properly briefed" on UK security.

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.

Britain and Mauritius denied on Wednesday media reports that London could end up paying double the amount in a renegotiated deal to retain a U.S.-British military base on Diego Garcia in the Indian Ocean.