For someone who’s supposed to be a details man, Rishi Sunak clearly doesn’t like being subjected to forensic interrogation.

At a painful appearance before the Infected Blood Inquiry on Wednesday, it didn’t help the prime minister’s mood when he was loudly heckled early on by members of the public listening to his evidence.

But it got worse and worse. And the finale, after nearly two hours, was excruciating for Mr Sunak when the inquiry chairman, Sir Brian Langstaff, delivered a powerful lecture that had the PM squirming in his seat.

Politics live: Infected Blood Inquiry ends with applause for chair’s message to Sunak

Actions rather than words were needed, said Sir Brian – a retired judge who has been credited with chairing this inquiry brilliantly.

It was a powerful climax to an afternoon of tension and tetchiness.

In a devastating call for the PM to act on paying compensation without more delay, Sir Brian declared: “Because if it troubles my conscience, I would think it will trouble the conscience of a caring government.”

Ouch!

It was emotional, it was dramatic and it was greeted by a rousing round of applause by the public in the giant hotel ballroom. A chastened and embarrassed Mr Sunak appeared to sink even lower into his seat.

Throughout Sir Brian’s stirring final words, Mr Sunak had sat like a naughty schoolboy being given a stern lecture by the headmaster.

The best he could say in response at the end was rather feebly to repeat his opening statement, that the blood scandal had been appalling – a statement of the obvious that will have done nothing to reassure those affected by it.

The heckling had come when the PM told the grieving families their long wait for compensation would have to continue.

There were no assurances or promises of a timetable about when the government will pay up.

We’d already seen the tetchy and prickly side to the PM’s character when he appeared before the Liaison Committee of senior MPs in the Commons three weeks ago.

At the beginning of that hearing, he haughtily announced he had a “pressing engagement” – which turned out to be nothing more than a photocall – in 90 minutes’ time.

And throughout that shifty and evasive performance at the committee, Mr Sunak gave the impression he wished he was somewhere else and couldn’t be bothered.

But that was nothing compared to his grumpy and at times surly manner here before the inquiry, in which his derisory body language revealed he was hating every minute.

Once again, like at the Liaison Committee, his answers were evasive. He wouldn’t give any pledges on compensation or promise legislation in the next King’s Speech due in November.

This time, instead of MPs, the PM faced just one interrogator – the counsel to the inquiry, the formidable Jenni Richards KC.

Unlike the theatrical and flamboyant KCs of the criminal courts, there’s nothing flashy about Ms Richards. But she’s just as effective and her probing got right under the PM’s skin.

He shuffled around in his seat, avoided eye contact with her as she asked her questions, looked down at his lap where perhaps he had a phone or iPad hidden from view.

When Sir Brian briefly mentioned the media, Mr Sunak glared at the press benches in the hall.

And, at one point, as the questioning got more and more uncomfortable, horror of horrors, the prime minister appeared to look at his watch. Surely not?

There were no pressing engagements – or even a photocall – to let him escape this time.

It’s never a good look. And an absolute no-no for politicians under pressure.

It was claimed George Bush Senior never recovered from looking at his watch during a TV debate with Bill Clinton in 1992.

Sir Brian’s dramatic peroration, on the other hand, will have enhanced his already well-established reputation as a dedicated and distinguished public servant who takes no prisoners when he’s in the chair.

His impressive chairmanship will also be seen as having created a model for the potentially devastating COVID inquiry to come.

And Mr Sunak will certainly need to be on top of the detail and less evasive when he appears before that inquiry.