Back in January 2022, Rishi Sunak made a promise to the British people and his party that he would stop small boat crossings.

Immigration – particularly illegal migration – was an issue that mattered to his voters and he insisted that he would be a prime minister of delivery.

Politics Live: Home secretary can’t guarantee migrants will be sent to Rwanda before next election

But the past few weeks have revealed the yawning gap between his rhetoric and reality as Mr Sunak now battles to keep his policy on track against the backdrop of a parliamentary party that looks like it could be about to go into freefall.

For he has ended the year more than 20 points behind in the polls, with net migration at a record high and his party on the precipice of a huge blowup over how he responds to the Supreme Court blocking plans to send asylum seekers to Rwanda.

The Conservative Party hasn’t just broken its 2019 manifesto promise to get migration below 250,000 but totally destroyed it, with migration at an estimated 745,000 in the year to December 2022.

Now the prime minister is trying to get back on track with a three-part migration plan.

On Monday, he published a five-point plan to get net migration back below 500,000 – the figure he inherited when he became prime minister last October. It’s still beyond the promise his predecessor Boris Johnson made to voters in 2019, but it is at least a start.

Far more thorny is how he might handle his most recent promise to voters – getting flights to Rwanda off the ground after the Supreme Court ruled last month that Rwanda was not a safe country.

On Tuesday the prime minister dispatched his new home secretary to Kigali on Tuesday to sign an update treaty which James Cleverly says should address the judges’ concerns.

But it is the third act, the emergency legislation to declare Rwanda safe and prevent further court challenges – that is the most politically significant for the prime minister who is struggling to maintain any authority over this party as the election gets closer but the gap between two parties in the polls remains desperately wide.

And now his MPs are in open revolt, with many fearful that he might fail to deliver on getting flights to Rwanda and another chunk fearful of what he might do to ensure they do. And both sides are now making their positions public as tensions over what Mr Sunak might do go into overdrive.

On the right of the party a trio of groupings – the European Research Group, the New Conservatives and the Commonsense Group – are teaming up tonight to discuss the policy and their position.

Perhaps up to 100 MPs in total, members I have spoken to are clear: the prime minister must include a controversial “notwithstanding” clause to disapply UK’s international and domestic human rights obligations when it comes to Rwanda policy.

Their cheerleaders are the former home secretary Suella Braverman and the immigration minister and once close ally of the prime minister, Robert Jenrick. One former cabinet minister told me on Tuesday that Mr Jenrick was now on resignation watch as he pushes for these measures against others in cabinet – Justice Secretary Alex Chalk and Attorney General Victoria Prentis – who are concerned about the UK withdrawing from international obligations.

“I think the PM has underestimated Rob on this. He thought that this stuff was all being pushed by Suella and Rob was just going along with it, and now he learns that it is actually what Rob believes in,” said the source, adding that Mr Jenrick could quit if the PM doesn’t embrace this option.

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And then this evening the One Nation caucus, which has a membership of 106 MPs, put out its own release arguing that the government can reduce migration without undermining the ECHR, and warned of trouble if the prime minister presses ahead.

“Leaving the ECHR..would be a mistake and doesn’t have public support,” said Stephen Hammond in a statement “Furthermore, moderates and mainstream Conservatives MPs may struggle to support the so-called full-fat deal.”

I think this is what you’d describe as being between a rock and hard place, with the prime minister destined to provoke a battle with a sizeable chunk of his backbenchers whatever he decides.

He will no doubt have front and centre of his mind his pledge to the British voting public when he decides how to proceed: how to make the legislation as watertight as he can in order to get those planes off to Rwanda by the spring.

The problem is, it’s not in his gift: his emergency laws must pass through both Houses of Parliament and then survive the inevitable legal wrangling that will follow.

When he made the pledge to stop small boats in January it seemed hard enough, and now he closes out the year with another promise he will not only struggle to keep but looks certain to further split his parliamentary party.