Boris misjudges the mood as mind wanders to petty point-scoring | Boris Johnson

A day that offered the country so much hope in a relentlessly grim year was one on which to put party politics on hold. At least that was the view taken by Keir Starmer in an appropriately subdued prime minister’s questions. He began – as had Boris Johnson – by expressing his gratitude to the scientists at Pfizer/BioNTech and the Medicines and Healthcare products Regulatory Agency for developing the coronavirus vaccine and for the speed at which it had been licensed, before asking for details of who would be the first 400,000 people to receive the jab when the first doses arrive later this week.

And at first it seemed – unusual, I know – that Johnson was taking a serious question seriously. There was none of the jingoism to which some of his ministers had fallen prey. The accident-prone Alok Sharma had tweeted that “in years to come we will remember this moment as the day the UK led humanity’s charge against this disease”. Er, I think not. The vaccine was developed by a Turkish immigrant couple in collaboration with a German pharmaceutical company. Matt Hancock, a late convert to Brexit, meanwhile was claiming it was only because the UK had left the EU that it had managed to approve the vaccine. Which was just untrue.

Instead, Boris was far more cautious in his approach, partly because he doesn’t know the details – he’s only had 10 months to work out how different doses of the vaccine might be rolled out – but also because he didn’t want the whole country to start acting as if we were all suddenly in the clear. This was just the start, he reminded MPs, sounding surprisingly clear-headed. There was a tiering system for the vaccine but he couldn’t yet say which care homes and over-80s would be first in line. Or how the vaccine would be delivered. Small steps and all that.

But Johnson could only maintain the act for so long. After not appearing particularly enthusiastic about Starmer’s offer of cross-party working to counter the disinformation of the anti-vaxxers, he completely ignored the Labour leader’s question on the conduct of the Arcadia Group directors. So what if a few more people lost their jobs? Just add them to the total. Instead, he went on the attack by accusing Keir of having failed to support the government in its new coronavirus measures the previous day.

This was the real Boris. Major Sulk unable to let go of any resentment. He’d gone through the charade of doing the statesman bit and wanted to squeeze in the few third-rate gags he had prepared that morning. Starmer refused to rise to the bait, instead observing that he had given his reasons for abstaining – it wasn’t that the new measures were too punitive, rather that they didn’t go far enough in offering financial support to industries under threat – and that when Johnson had abstained as foreign secretary over the third runway at Heathrow, he had done so under the guise of a pointless £20k round trip to Afghanistan.

That clearly stung Johnson, but he wouldn’t let up. All thoughts of the vaccine were long erased and all he had on his mind was petty point-scoring. “I’d take him more seriously if he had voted with the government,” he continued, conveniently forgetting that if Labour had not abstained then he would have lost Tuesday night’s vote, and that he had already forgiven his own backbenchers who had either voted against him or abstained, on the grounds that they had been acting out of a strong sense of principle. The irony was lost on Boris but not on the rest of the house.

“He used to be Captain Hindsight,” Johnson blundered on. “Now he’s General Indecision.” If nothing else it was an act of insubordination coming from Major Sulk. The gag probably sounded better when he had practised it in the shower. As it was, it raised only a few half-hearted laughs from the most loyal Tory backbenchers. Starmer’s instincts had been correct and Boris had misjudged the mood. This was a day for the country to come together, not for the leaders of the two main parties to squabble like children. Somehow, without even realising it, the prime minister had again snatched humiliation from the jaws of defeat.

At the Downing Street press conference later in the afternoon, it sounded at first as if Johnson had had second thoughts about his lack of warmongering nationalistic rhetoric at PMQs. In his opening remarks, he waffled on about the “searchlights of science” hunting down the invisible enemy, “biological jiu-jitsu”, how Britain had pioneered the idea of vaccination and how the UK had led the way by being the first country to buy the Pfizer/BioNTech vaccine.

But after Simon Stevens, the chief executive of NHS England, had spelled out the logistical problems of rolling out the vaccine to those who needed it most, and Jonathan Van-Tam, the deputy chief medical officer for England, said how moved he had been by the truly global effort to develop a vaccine – he even squeezed in another of his legendary train analogies, along with observing that the vaccine wasn’t some yoghurt that could be taken in and out of a fridge (he should see the sell-by dates of some of the stuff in our fridge) – Boris calmed down a little.

So much so that when twice pressed to say that we basically owed our lives to Brexit and that we would never have got the vaccine if we had stayed in the EU, he declined both times. Even though he was probably dying to say yes. Come the end he was even sounding vaguely like a prime minister. It won’t last, so make the most of it while you can.

• Join John Crace and Marina Hyde as they look back at a political year like no other. Thursday 10 December, 7pm GMT, 8pm CET, 2pm EST. Book tickets here.