I’ve noted before that the surest way to predict Rishi Sunak’s next move is to ask yourself: “What would I do if I were a total idiot?” Resign from Boris Johnson’s government but also refuse to criticise him? Brilliant! So it was inevitable that when he repeatedly told a prime time TV debate audience that Labour were going to put taxes up by £2,000 — an effective attack which he repeatedly banged home — that he would turn out to have found some way to mess it up.

These, he told us, weren’t Conservative estimates, they were estimates from neutral Treasury officials. They were numbers you could take to the bank. Uninformed viewers might have wondered if this was really right. Informed ones would have known that they are cooked up by Conservatives asking questions along the lines of: “These free school meals — what if they were all served on solid gold plates? What would that cost?”

You don’t get to be a very senior civil servant without being pretty careful about what you put your name to

But no matter. Sunak is a leading politician, the actual prime minister, in fact. He knows the importance of staying on the right side of the line that separates “misleading” from “untrue”. If he was saying the Treasury had signed the numbers off, there was no way … Hold that thought. Remember to approach this question like a total idiot. What would a total idiot do?

We would find out the answer to this on Wednesday morning. Claire Coutinho, the Energy Secretary, was on the Today programme, punching the Labour tax bruise. Keir Starmer, she said, had been “asked 12 times” about the number. “It would have been so easy for him to say no, but he didn’t.”

“Well,” interjected the BBC’s Justin Webb, “he did say it was nonsense.” Coutinho wasn’t going to be blown off course by such trivialities: “He was asked 12 times.”

The important point, she went on, was that the number came from “Treasury officials.”

Was that right, asked Webb. Hadn’t the numbers been generated by Conservative officials guessing what Labour policies might be? “I’m going to have to heavily push back on that,” Coutinho said, before not in fact pushing back on it at all.

Anyway, she went on, “this is something that’s been signed off by the Treasury, by the Permanent Secretary of the Treasury!”

This was quite a claim. You don’t get to be a very senior civil servant without being pretty careful about what you put your name to. Webb queried the point: “You’re saying the Permanent Secretary of the Treasury would not have signed this off if it was dodgy?”

Coutinho was firm: “They will not sign off things which are dodgy.”

And on this, at least, it turns out she was speaking no more than the truth. Because, I remind you once again, the thing you have to say to yourself is: How would I approach this if I were really just very bad at politics? What is the thing that I would say if I were the sort of idiot who will find a way to mess up even the most basic task? A proper, thorough-going numpty?

Can you guess the next thing that happened? Remember, we’re talking about idiots here. Shouldn’t be allowed out on their own, and certainly not put in front of the cameras. Real dimwits.

The prime minister may be an idiot, but he’s quite a useful one

Twenty-six minutes after Coutinho had told us that the Permanent Secretary of the Treasury had put his name to the Conservative figures, the BBC tweeted a letter from — I bet you can’t guess who — the Permanent Secretary of the Treasury! “Civil servants were not involved in the production or presentation of the Conservative Party’s document,” he wrote, “or in the calculation of the total figure used.” The numbers, he said, “should not be presented as having been produced by the Civil Service.”

You may think this makes Sunak and Coutinho look pretty silly, and you’d be right. But to understand why they were guilty of weapons-grade daftness, you had to look first at the bottom of the letter, where the civil servant said he’d reminded ministers not to attribute the numbers to his department, and then at the top, where it was dated two days ago. So he’d written to Labour, and told the Tories he’d done so, and Sunak had gone ahead and used the numbers anyway. What, as I say, would an idiot do?

The real mystery is why Labour didn’t release the letter until Wednesday morning. Had they been properly organised, Starmer would have had a copy of it in his pocket at the debate. The most likely explanation is a cock-up, but we shouldn’t rule out the possibility that the opposition has been spooked by talk of the Conservatives replacing Sunak mid-campaign. From their perspective, the prime minister may be an idiot, but he’s quite a useful one.