A US senator has launched an extraordinary attack on Keir Starmer over the government’s plan to hand over the Chagos Islands to Mauritius.
John Kennedy suggested the prime minister must be on drugs to back the deal - telling him: “Put the bong down.”
The islands are a British overseas territory in the middle of the Indian Ocean and are also home to a UK-US naval base at Diego Garcia.
In October, the government announced that it was handing over sovereignty of the islands to Mauritius, but that the base would remain under British and American control on a 99-year lease.
Ministers have said that an advisory ruling by the International Court of Justice in 2019 - subsequently backed by the United Nations - that the UK has no claim to the islands means that the territory must be given to Mauritius.
Starmer had wanted to get the handover finalised before Donald Trump - who is known to oppose the deal - was sworn in as president, but failed to do so.
It is now unclear whether the US president will step in to block the handover from taking place.
Making clear his own opposition to the deal, Kennedy, the Republican senator from Louisiana, said it was “bone deep down to the marrow stupid”.
“Because the United Nations wants the United Kingdom to feel guilty, they want to give our military base and their military base to Mauritius,” he said.
“Now, the prime minister of the United Kingdom can stop this, and Marco Rubio, our new Secretary of State, is against it. And I haven’t talked to him directly, but I think President Trump is against it.
“The United Kingdom is our friend. I went to school there for a while. I love them and I want to see the prime minister do well, but he needs to put down the bong. He needs to put down the bong.
“This makes absolutely no sense, and it’s going to be a big part of his legacy if he gives away this island and our military base to, in effect, what will eventually be China.
“So I would say to the prime minister tonight I don’t mean any disrespect. I want to say this respectfully. I shouldn’t have said the bong part, I take it back. Please Mr prime minister, don’t do this. Don’t do this. We’ll stand with you in telling the United Nations, who’s so upset with you, to go fill out a hurt feelings report because we’re not doing it. We’ll stand with you.”
It has been reported that the UK has agreed to pay Mauritius ÂŁ90 million a year as part of the deal, which works out at ÂŁ9 billion in total.
But Navin Ramgaloom, the Mauritian prime minister, said last week that the UK could end up paying his country twice as much as originally planned.
He told the Mauritian parliament: “The British prime minister informed me he intends to push ahead with the agreement reached between Mauritius and the United Kingdom. We remain confident it will reach a speedy resolution in the coming weeks.”
Ramgaloom said the deal has now been amended so that the UK payments are linked to the rate of inflation.
He said: “They had agreed to a package for 99 years, but not inflation-proof. The exchange rate — because it’s in dollars — would be fixed once and then last 99 years. How can that be? Any ordinary fifth-form, sixth-form student would agree that you know inflation exists.
“What is the point of having money and having half of it by the end? This is what would happen — we made the calculation.”
His comments suggest that the deal could end up costing the UK £18 billion, although Downing Street sources have rejected that calculation.”
A spokesman for Starmer said: “I’m not going to give a running commentary on the deal. Once an agreement is reached, further details of the treaty will be put before both houses [of parliament] for scrutiny and treaty ratification in the usual way.”
He added: “Our position remains that finalising a deal means we can secure strong protections, including from malign influences, that will allow the base to continue to operate.
“We’ll only agree to a deal which is in the UK’s best interests and protects our national security.”