The cost of the Chagos Islands deal is equivalent to more than a decade of winter fuel payment savings, according to new analysis.

The research found that the upper estimate of £18 billion matches the money the Labour Government expects to save from scrapping the cold weather allowance for most OAPs for 12 years.

Sir Keir Starmer plans to cede sovereignty over the British Indian Ocean Territory to Mauritius, but then pay to lease back the UK/US Diego Garcia military base.

John O'Connell, chief executive of the TaxPayers' Alliance, which carried out the analysis, said: "The cost of the Chagos deal adds insult to an already disgraceful and immoral betrayal of British interests.

"The Government is surrendering sovereign territory and forcing taxpayers to foot the bill, all while families and businesses suffer under the consequences of the chancellor's economic vandalism.

"The Prime Minister needs to stop appeasing lawyers and international bureaucrats and end this handover of British sovereign territory immediately."

A deal has been reached at a reported cost of £9 billion although the Government has not confirmed any figure.

The UK has denied suggestions the cost could spiral to £18 billion after the Mauritian Prime Minister Navin Ramgoolam said payments would be inflation-linked.

The Mauritian government subsequently issued a statement clarifying Mr Ramgoolam's comments, insisting it had not claimed the cost of the deal would double.

The lower £9 billion estimate exceeds the combined costs of various public sector projects, including NHS frontline digitisation and the plan to crack down on abuses of the asylum system, according to the research.

It comes as the Government is facing an ongoing backlash from opposition parties over the plan to give away the archipelago.

Prime Minister Sir Keir Starmer has insisted that without a deal national security could be at risk.

The Foreign, Commonwealth and Development Office has been contacted for comment.