In a revelation branded a “national scandal” by Labour, the National Audit Office (NAO) said the plan could cost taxpayers nearly £2 million for each of the first 300 asylum seekers sent to the east African nation.

The Home Office had so far refused to say how much more money, on top of the £290 million already confirmed, the UK has agreed to pay Kigali under the stalled plan but a NAO report uncovered millions more in spending including £11,000 for each migrant’s plane ticket.

The Prime Minister on Friday defended his flagship asylum scheme, which is central to his pledge to stop migrants crossing the Channel in small boats.

Speaking during a visit to Scotland, Mr Sunak told reporters: “The current situation is unsustainable and unfair. Taxpayers are already forking out millions of pounds a day to house illegal migrants in hotels across the country, that’s not right. That’s why I made stopping the boats one of my priorities.

“I’m pleased that we’ve made progress, last year the numbers were down by a third.”

He continued: “In order to fully resolve this issue we need to have a deterrent. We need to be able to say if you come here illegally, you won’t be able to stay, we can remove you to a safe country.

“That’s why the Rwanda scheme is so important. It’s a worthwhile investment and I’m determined to see it through.”

No asylum seeker who has arrived in the UK via unauthorised means has been removed to Rwanda under the policy because of the legal challenges that resulted in the Supreme Court finding the scheme unlawful.

Even if no one is deported in the future, Mr Sunak has already agreed to pay £370 million over the five-year deal.