Ministers signed the deal with the African nation in 2022, with the aim of deporting asylum seekers to the country if they came to the UK via illegal means - such as small boat Channel crossings.

But while the price tag for the scheme had been set at £140m, another £100m has been paid to the Rwanda government since, with a further £50m due to be paid out later in the year.

Politics live: New poll makes grim reading for Sunak

There has been furious reaction from opposition parties, with Labour dubbing it a "total farce".

However, Downing Street has insisted the original agreement stated the deal "involves subsequent funding".

And Home Office minister Lord Sharpe told peers it was "good value for money", saying it equated to the cost of housing asylum seekers in hotels for 30 days.

The new figure came to light after requests from both the Public Accounts Committee and the Home Affairs Committee for more detail from the Home Office permanent secretary, Sir Matthew Rycroft, after he appeared in front of them in recent weeks.

In a letter to the committee chairs, Sir Matthew said it had now been "agreed" by ministers to disclose the numbers, with the £100m paid in April and the £50m still to come.

In an angry response, the two chairs - Labour MPs Dame Meg Hiller and Dame Diana Johnson - accused the civil servant of an "extreme lack of respect" for committees, adding that they "would have expected more transparency" from him in his previous appearances and saw "no reason" for having avoided the topic.

As well as demanding Sir Matthew appeared in front of them on Monday, the chairs said they now wanted to see quarterly updates on the funding for the scheme going forward.

A row has also broken out over who signed off the additional cash - Prime Minister Rishi Sunak or his now former home secretary, Suella Braverman.

Downing Street said it was Ms Braverman who gave the payment the green light. However, friends close to the ex-minister insisted it was approved by Mr Sunak himself.

This latest controversy over the much troubled policy came just hours after the prime minister vowed to "finish the job" of reviving the Rwanda plan - despite the prospect of a bitter parliamentary battle.

The government unveiled new legislation on Wednesday to address the problems cited by the Supreme Court when it ruled the scheme unlawful last month.

The bill compels UK judges to treat Rwanda as a safe country for asylum seekers, and disapplies some aspects of the Human Rights Act in an attempt to appeals against deportations.

However, some of the right of the Conservative Party - including former immigration minister Robert Jenrick, who resigned his post in protest - believe the legislation doesn't go far enough.

They instead want the government to disregard the entire Human Rights Act, as well as include extra powers to dismiss challenges under the European Convention of Human Rights (ECHR).

Writing in the Telegraph, Mr Jenrick doubled down on his argument, saying the UK needed to leave the "complex web" of international human rights treaties if it wanted to tackle illegal migration.

He said the "dangerous and completely unnecessary" Channel crossings had pushed the UK "beyond breaking point and left our border security in disarray".

And he claimed the "outlook was deteriorating", with new conflicts that could see even more asylum seekers heading to our shores, and rules allowing every arrival to lodge a personal claim set to "place the courts under unsustainable pressure".

"Having promised to do whatever it takes to stop the boats, the goal now seems to have been reduced to delivering some symbolic, half-filled flights, taking off in the spring of next year," added the former minister, warning that for the Rwanda plan to work, people needed to be "removed at scale and within days of illegally stepping onto our shores - anything less than this and the boats will keep coming".

Mr Jenrick also predicted immigration would be a "defining issue of 21st century politics", concluding: "Centre-right parties across Europe have a choice: deliver on the mainstream concerns of ordinary people when it comes to immigration, or face their red-hot fury at the ballot box."

The new law will be voted on next Tuesday. But with opposition parties already vowing to vote against it and less than 30 Tory rebels needed to kill the bill off, it could be a tough battle for Mr Sunak.