“I’m a Conservative, a Brexiteer and a Unionist,” Rishi Sunak announced. It was one of those straightforward clap-lines that the prime minister somehow manages to deliver to silence from his own side. He really does think that he’s all of these things, but no one else seems to quite believe him.

The only way you can find out if it’s alive or dead is to open it

The issue at hand was — and even as I prepare to type the words I feel I should apologise — the Northern Ireland Protocol. All you really need to know about this is that Boris Johnson promised everyone that he’d solved it, and it turned out — brace yourselves — that he was actually just making that up so he could get what he wanted. This was — and again, you may wish to sit down — transparently obvious at the time, but Conservative MPs are pretending they’ve only just noticed.

Sunak has his own trademark approach to the problem, which is to let it be known that he’s on the brink of a solution which will satisfy everyone if they saw it, but which they’re not allowed to see, in case they’re not satisfied.

To put it another way, it’s as if his deal is in a box, and the only way you can find out if it’s alive or dead is to open it. But unfortunately the box is nailed shut and locked in a safe, which has been dropped to the bottom of an ocean. So you’ll just have to take his word for it that the contents are terrific.

The faces of his MPs behind him as he assured them that they’d like his deal were carefully immobile. Sir Bill Cash, a man who can detect a concession to the European Union through a bricked-up door at a thousand yards, was rigid. High up on the benches opposite him Sir Jeffrey Donaldson, leader of the Democratic Unionists, was trying to work out how he was going to be stitched up this time. Next to Donaldson, the Sphinx would seem rubber-faced.

Tories quite liked that, and shouted for more

Sunak’s comments were prompted by Keir Starmer, who had decided to use Prime Minister’s Questions to helpfully poke this particular hornet’s nest. His approach was to remind Sunak of the things that Johnson had promised. Tory MPs get upset when he does this, and start shouting things at him, as though mentioning the pledges on which they were elected is a kind of underhand trick. You could feel sorry for Sunak who is stuck, like so many before him, clearing up Johnson’s mess, were it not that he did quite a lot to help him get elected.

For now, though, Sunak is just about managing to keep the ball in the air. Starmer put it to him that at some point he’d have to accept a role for the European Court of Justice in Northern Ireland’s affairs. The prime minister tried his best to be dismissive, saying that the Labour leader wanted to “give the EU a blank cheque and agree to anything it offers”. He drew himself up. “It is not a strategy; that is surrender.”

Tories quite liked that, and shouted for more. It’s Starmer’s bet that they’ll be less happy when they find out what the deal looks like. “The sound you hear is Conservative members cheering the prime minister pulling the wool over their eyes,” he said, and asked if Parliament would get a vote on the deal. Sunak replied that the House will “express its view”, though it’s not clear what that means. Donaldson sat with one arm across his chest, his hand on his chin, apparently deep in thought.

If the DUP are hard to read, Theresa May, sat as ever directly behind Sunak, is an open book. This is a woman you could take to the cleaners at poker. As the prime minister turned his attention to his planned law to definitely stop migrants crossing the Channel, she rolled her eyes. “We are working at pace on the legislation,” Sunak said. “It is important that it works.” May nodded at that, but her raised eyebrows suggested that she thought it was unlikely that it would, in fact, work.

If we were in any doubt about her feelings, Sir Bill Wiggin raised the question again. Could the Small Boats Bill come to parliament next week, he asked. In the course of his 23 words, May’s face went through the most amazing range of expressions that can fairly be summarised as: “Where do we find these morons?”

Perhaps she’s wrong, though. Perhaps the Small Boats Bill will be drafted so effectively that, upon hearing of it, people smugglers give up their lives of crime and go and volunteer at food banks. Perhaps Sunak’s Brexit deal will be endorsed by Donaldson and cheered by Cash. He’ll have to let us see it first.