When the deal was signed, after years of talks, Sir Keir and his then-Mauritian counterpart Pravind Jugnauth called it a "seminal moment in our relationship and a demonstration of our enduring commitment to the peaceful resolution of disputes and the rule of law".

But in his election campaign, Ramgoolam and his allies in the Change coalition described the agreement as a "sell-out" motivated by desperation ahead of the vote.

Arvin Boolell, the newly appointed minister of agro-industry and fisheries, had been more specific about the objections in his comments on Monday.

He criticised the former prime minister for granting the UK a long lease over Diego Garcia - he said it was 200 years, though the publicised timeframe was an initial period of 99 years.

The Change coalition are not the only ones with reservations about the deal - Marco Rubio, US President-elect Donald Trump’s pick for secretary of state, said in October that the deal posed a "serious threat" to US national security by giving the islands to a country allied with China.

Some groups representing the interests of Chagossians have also expressed disquiet, saying they were excluded from the negotiations.

The British prime minister and his Foreign Secretary, David Lammy, have defended the agreement as a "good deal".

"I'm very, very confident that this is a deal that the Mauritians will see, in a cross-party sense, as a good deal for them," Lammy said on Thursday.

The deal is still subject to the finalisation of a treaty.

Details of the treaty's legal text are being worked out and it is expected to go before the UK Parliament for scrutiny next year.