Sir Keir Starmer has been forced to delay legislation that would hand the Chagos Islands back to Mauritius after Conservatives tabled a wrecking amendment in the House of Lords.

The legislation was expected to be debated on Monday, but was delayed on Friday night after the Conservatives claimed it could violate a 60-year-old treaty with the US that enshrines British sovereignty over the archipelago.

President Trump turned against the Chagos deal this week, saying that Britain’s plan to hand the Indian Ocean territory to Mauritius was “an act of great stupidity”.

US President Donald Trump leaving the World Economic Forum in Davos.

Trump in Davos this week

LAURENT GILLIERONEPA

Ministers said in December that the UK and the US were in talks about updating a 1966 agreement on the Diego Garcia military base in light of the new Chagos deal.

But on Friday the Conservatives tabled a motion calling for the treaty’s ratification to be delayed to allow the talks to conclude.

Labour, which does not have a majority in the Lords, has now delayed a planned debate in the second chamber amid fears the government would be defeated.

However, the party said the bill would proceed in the coming weeks. Labour is expected to try to garner support from crossbench peers and the Liberal Democrats.

“It is simply a response to Tory peers having flexed their much greater numbers in the House by tabling a wrecking amendment to a government bill just hours before the end of business ahead of a scheduled debate on the next sitting day,” a Labour source said.

British Prime Minister Keir Starmer speaking at a podium with a UK flag in the background.

Sir Keir Starmer has faced criticism over the deal

TOLGA AKMEN/EPA

Dame Priti Patel, the shadow foreign secretary, said it was a “major victory for everyone standing against Keir Starmer’s disgraceful Chagos surrender”.

She said: “In the face of relentless Conservative pressure, Labour have pulled their shameful bill from Monday’s order paper.

“The deal, which hands British sovereign territory and £35 billion to an ally of China, should be dropped altogether. The Conservatives will continue to fight the surrender every step of the way.”

The agreement struck in December 1966 between the UK and the US said the Chagos Islands “shall remain under United Kingdom sovereignty”. The treaty, registered with the United Nations, was agreed as part of discussions around the use of Diego Garcia by the UK and US for defence purposes.

Asked about the effect of the previous deal on Starmer’s new agreement, Baroness Chapman of Darlington, the Foreign Office minister, said the UK and US were discussing the matter.

Baroness Chapman of Darlington leaving the weekly Government cabinet meeting.

Baroness Chapman of Darlington

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She said in December: “The agreement between the UK and Mauritius secures the important UK-US military base on Diego Garcia.

“The agreement was tested at the highest levels of the United States’ security establishment, across multiple agencies, and it has been backed by our key allies and international partners, including the US and all our Five Eyes partners.

“Talks are ongoing to update the UK-US Exchange of Letters on the operation of the Diego Garcia base.”