David Lammy will face questions from MPs angry about the decision to give up sovereignty over the Chagos Islands, later on Monday.
The Foreign Secretary’s appearance in the Commons comes as No 10 said the decision should not be viewed as a signal of movement on other disputed territories, including the Falkland Islands and Gibraltar.
Mr Lammy will update Parliament on the announcement about the islands, known as the British Indian Ocean Territory (BIOT), which was made while the Commons was not sitting during the break for party conferences.
Downing Street said the deal to give up sovereignty over the BIOT was because of the “unsustainable” legal position and had no impact on other sovereignty disputes.
The International Court of Justice ruled the UK’s administration of the Indian Ocean territory was “unlawful” and must end, a judgment backed by a United Nations vote in 2019.
The Prime Minister’s official spokesman would not be drawn on the cost to the UK taxpayer of the deal, in which Mauritius will be given sovereignty over the islands, with a 99-year agreement, to secure the strategically important UK-US military base on Diego Garcia.
The spokesman said: “The Government inherited a situation where the long-term secure operation of the military base at Diego Garcia was under threat with contested sovereignty and legal challenges, including through various international courts and tribunals.
“You will be aware that the previous government initiated sovereignty negotiations in 2022 and conducted a number of rounds of negotiations.
“This Government picked up those negotiations and has reached an agreement, which means that for the first time in over 50 years, the base will be undisputed, legally secure, with full Mauritian backing.”
Asked why the BIOT should not be seen as a precedent for other sovereignty disputes such as the Falklands and Gibraltar, the spokesman said: “It’s a unique situation based on its unique history and circumstances, and has no bearing on other overseas territories.”
The spokesman added: “British sovereignty of the Falkland Islands or Gibraltar is not up for negotiation.”
Shadow foreign secretary Andrew Mitchell has described the agreement as a “bad deal for Britain”.
He told Sky News’s Sunday Morning With Trevor Phillips programme: “This is definitely, from what we have seen, not the deal the last Conservative government would have done.”
He added: “We need to know about what protection there is against Chinese encroachment into the archipelago, we need to know what money is being provided by the British taxpayer. We need to probe the terms of the lease.”
The International Court of Justice had previously ruled the UK’s administration of the Indian Ocean territory was “unlawful” and must end, a judgment backed by a United Nations vote in 2019.
