Former defence secretary Sir Grant Shapps and ex-Tory leader Iain Duncan Smith have signed a letter along with other politicians and former senior military officers to Donald Trump asking him to intervene to block the Chagos deal.
Serious concerns remain over the impact on UK and US defence and security with threats to the operational ability of the Diego Garcia case in the Indian Ocean, which Sir Keir Starmer’s government claims it is protecting.
The US president has already given the deal with Mauritius his blessing but it was sent to the White House as Sir Keir Starmer pushed through a vote on ratifying the deal in the House of Commons.
A bad-tempered debate over the deal among MPs saw claims that the government’s legal case for handing over the islands had “collapsed”.
MPs pointed out that claims the UK would be subject to legal challenges through the United Nations Convention on the Law of the Sea (UNCLOS) had already been dismissed.
As previously revealed by The Independent, the government had used UNCLOS as its main legal case for suggesting the UK and US could lose access to the crucial military base on Diego Garcia.
But the UK is protected from UNCLOS because it has an opt out concerning “military activities, including military activities by government vessels and aircraft engaged in non-commercial service, and disputes concerning law enforcement activities” in article 28 of the agreement.
In the letter from British politicians and retired military personnel, they warned Mr Trump that handing the islands would mean Mauritius could veto the allies from taking nuclear weapons there.
They said: “If the UK and US are prohibited from storing nuclear weapons at Diego Garcia, this will have significant consequences for our strategic interests, defence capabilities and the effectiveness of our nuclear deterrent.
“Mr President, you have built your reputation on refusing to cede strategic ground to those who would weaken America. We urge you to use your influence, publicly and privately, and your prerogatives under the US-UK defence agreement of 1966 to oppose this surrender and to ensure that Diego Garcia remains exempt from any constraint under the Pelindaba Treaty.”
The Labour government is attempting to push through the deal before a human rights challenge by Chagosans, who were excluded from the talks and will only have limited rights to return to the islands, can be heard in October.
It is estimated that the cost of the deal over 99 years will be £30bn to the taxpayer.
But the debate focussed on the threat of international rulings degrading the ability of the UK and US to use the base.
Defence secretary John Healey admitted that UNCLOS was the biggest concern.
He told MPs: “Within a few weeks international rulings will start to weaken our ability to maintain and control our full operational sovereignty over Diego Garcia.
“Within just a few years we expect that to be at a point in which it compromises our ability to continue the operation that are so essential to protecting people at home here and also protecting our forces when they deploy around the world.”
But numerous Tory MPs disputed the legal case he was outlining which makes the deal essential.
Shadow armed forces minister Mark Francois said: “During today’s Commons Debate on Diego Garcia, the government’s legal case collapsed, under close scrutiny. They finally revealed that the “legal threat” to justify their £35 billion surrender deal is based on the UNCLOS Treaty – from which we in Britain already have a clear opt out for “disputes concerning military activities” in Article 296. The whole case is a sham, as Parliament has today discovered.”