Conservative peers have launched a last-ditch attempt to stop Sir Keir Starmer from giving the Chagos Islands to Mauritius.

Tories in the Lords have put forward a fatal motion to block the Chagos Islands treaty signed by Sir Keir last month.

Lord Callanan, the shadow Foreign Minister in the Lords, put forward a motion demanding that the Government "should not ratify the agreement", citing cost and security concerns.

The peer told The Telegraph: "Spooked by a last-minute legal fight, the Government's unnecessary political decision to sign away our sovereignty over the Chagos Islands will cost the British taxpayer £30billion and put our strategic defence interests at risk."

Protesters outside the High Court in central London holding the Chagos flag

The deal will give up British sovereignty over the archipelago, known in the UK as the British Indian Ocean Territory, and see the UK pay Mauritius £30billion over 99 years.

It is the first time a Lords front bench has sought to use the Constitutional Reform and Governance Act, passed in 2010, to block a treaty.

The Lords motion cites "concerns about the cost of the agreement, the absence of any legal requirement to conclude such an agreement, its impact on international security, the lack of any meaningful consultation of the Chagossian people, and recognising the right of Chagossians to be registered as British Overseas Territory citizens under the Nationality and Borders Act 2022".

A fatal motion, if passed, halts the process of the legislation, and the Government would ordinarily have to start again.

Lord Callanan has made the intervention

Meanwhile, Misley Mandarin, a British Chagossian, is being supported by the Great British PAC, a conservative movement headed by former Reform deputy leader Ben Habib, to take legal action against the Government.

The organisation said it had raised enough money to launch a review and cover legal fees, but is seeking another £20,000 to underwrite the case.

Mandarin said: "We were evicted from our homeland by a past Labour government. Now the current Labour Government is doing something even worse – stripping us of our right to self-determination."

Habib said: "This is not just a treaty, it's a national betrayal, done behind closed doors and without a democratic mandate. But it's not too late to stop it."

Former Reform Deputy Leader Ben Habib has backed the motion

The Government's announcement of the Chagos Islands deal was temporarily delayed after a legal challenge was launched by Beatrice Pompe, a Chagossian.

However, the last-minute bid was dismissed by the High Court, allowing Sir Keir to sign the agreement and announce that a deal had been done.

If a subsequent vote passes, the Government could be forced to make a statement in the Commons to explain why it is ignoring the upper chamber.

In the case of the Constitutional Reform and Governance Act, a minister can choose to override the Lords by making a statement in the Commons.