Rishi Sunak’s promised new treaty with Rwanda appears unlikely to be ratified before the new year as he races to get flights under his grounded asylum policy in the air in the spring.

The deal that the Prime Minister hopes to sign after the Supreme Court defeat had been billed for as soon as Monday but is now not expected before the autumn statement on Wednesday.

Mr Sunak has pinned his hopes on a new legally binding pact with Kigali alongside emergency legislation after the Supreme Court ruled the policy unlawful on November 15.

Downing Street had said in the hours after the defeat that the deal would be laid before Parliament in the “coming days” so removal flights can take off “as soon as possible”.

But Whitehall sources said the treaty is not expected to be published until some time after Chancellor Jeremy Hunt details his set-piece financial announcement on Wednesday.

With the Commons due to rise for its Christmas recess on December 19, there are not enough sitting days to ratify the treaty before the new year under the current schedule, with No 10 saying at least 21 are required.

Labour’s shadow home secretary Yevette Cooper said: “This is just further chaos from the Conservatives. Further delay to a plan which has already failed.

“This is yet more hot air, rhetoric and chaos from a Tory party clearly unable to stop the criminal gangs or deliver their promise on small boats.”

Downing Street said that “further detail will be set out in the coming days”, as one source sought to downplay any suggestion of a delay to signing off the deal with Rwanda.

On Sunday, Mr Hunt gave his backing to Mr Sunak to solve the “fearsomely complex” challenge of getting the Rwanda asylum policy to work, as the pair set sights on a first flight in the spring.

Sacked home secretary Suella Braverman has been increasing the pressure, arguing his “tweaking and fine-tuning” will fail to get flights off before the election.

Mr Hunt conceded the policy “isn’t easy stuff” but said Mr Sunak is the “most persistent, the most determined prime minister I have ever worked with”.

He suggested Mr Sunak is more determined when it comes to solving problems than Lord David Cameron, the former prime minister who returned from the political wilderness to become Foreign Secretary in the reshuffle.

“I enjoyed working with David Cameron very much, but when it comes to solving fearsomely complex problems I have never worked with anyone as phenomenal as Rishi,” Mr Hunt told the BBC’s Sunday With Laura Kuenssberg.

“I think we will see that, because I do think, when you interview me next year, we will be having a discussion about how we have succeeded in this plan, and I will be saying ‘look, it wasn’t easy, we kept at it, but that is what we promise to do’.”

The source did not expect any problems getting Kigali to sign off on the treaty, believing that the emergency legislation is the greater challenge.

In an interview with the Mail on Sunday, Mrs Braverman said the Prime Minister has lacked the “moral leadership” to deal with pro-Palestine marches, which she has described as “mobs”.

She welcomed Mr Sunak’s plans for emergency legislation but said the changes need to be “meaningful”, adding that “tweaking and fine-tuning is not going to cut it … and we will not get flights off before the next general election”.

What we are saying is in the end... it must be Parliament, elected representatives in Parliament, not foreign judges, who decide who can come to this country

The Tory MP said elements of the domestic and international human rights legislation need to be excluded, as some colleagues on the right want the European Convention on Human Rights to be ditched altogether.

However, Mr Hunt told the BBC that “at this stage” he does not believe following Vladimir Putin’s Russia in exiting the ECHR is necessary.

“What we are saying is in the end… it must be Parliament, elected representatives in Parliament, not foreign judges, who decide who can come to this country,” he said.

“We don’t believe it will come to that at this stage, we think there are ways we can avoid that, we don’t want to do that.”

Former Supreme Court judge Lord Sumption argued the Rwanda plan is “probably dead” in its current form and believes judges in the European Court of Human Rights would probably agree with the top justices in the UK who blocked the plans.

“It will investigate safety for itself and probably arrive at a conclusion very similar to that of the Supreme Court,” he told Sky’s Sunday Morning with Trevor Phillips.

The five justices ruled on Wednesday that the policy was unlawful, citing concerns that Rwanda could send genuine refugees to the countries they fled from.