What possible lines of defence could the Prime Minister come up with after the leaking of footage showing his Downing Street aides joking about a party he has spent the past week insisting didn’t happen? From the moment ITV broadcast the clip, the No. 10 Christmas party was a dead cert as the sole topic at today’s Prime Minister’s Questions. Almost as much of a certainty was that Boris Johnson would respond by getting other people to take responsibility for him.

This is precisely what he did, using a question prior to his exchanges with Sir Keir Starmer to try to get out in front of the matter. He told the chamber he was ‘also furious to see’ the video, and ‘I apologise unreservedly for the offence that it has caused up and down the country and I apologise for the impression that it gives’. A change in stance from the Prime Minister: he hoped that the story would just fizzle out if he toughed it out with denials. What he then said followed the pattern Johnson has always stuck to when in deep crisis: to get someone else to carry the can. He said: ‘I have been repeatedly assured since these allegations emerged that there was no party and that no Covid rules were broken. And that is what I have been repeatedly assured.’

So the Prime Minister would rather claim to the Commons that he has no idea what is going on within No. 10 and that his own staff could have been lying to him. In order to find out whether the latter is the case, he has asked the Cabinet Secretary to launch an investigation, and promised the chamber that necessary disciplinary action would be taken. He said he would ‘place a copy of the Cabinet Secretary’s report in the library of the House of Commons’. That’ll learn them.

It was not a dead cert that Sir Keir Starmer would make the most of this crisis. He has had a tendency to act as a commentator rather than agitator in these circumstances, but today the Labour leader did force the Prime Minister to make further concessions. His most consequential question involved him demanding that he hand over ‘everything the government knows about parties in Downing Street to the Metropolitan Police’. Johnson replied: ‘Of course we will do that.’

Starmer was able to drive home a theme he has been developing for a long time, saying in his first question that ‘millions of people now think the Prime Minister was taking them for fools and that they were lied to’. He also once again used his experience outside parliament to mock one of the many poor ministerial defences from the past week, ridiculing Dominic Raab for suggesting the police wouldn’t investigate a crime that happened a year ago. ‘Well I ran the Crown Prosecution Service and could just tell him that is total nonsense.’ He had a good fact for the chamber too: today Westminster magistrates court is seeing prosecutions of Covid rule breaches from a year ago, including people who hosted parties.

Johnson’s repeated riposte throughout the pair’s exchanges was weak. He accused the Labour leader of ‘playing politics’. This is always a poor line from a fellow politician because it suggests that politics itself, the act of getting things done, representing people and scrutinising the decisions of others, is a dirty thing. But it is particularly incredible from a politician for whom politics has often seemed like a spell of the Eton Wall Game: something to churn through, knocking opponents and objectors asunder and enjoying it all the while.

He was offered some respite, not from a loyal backbencher on his own side, but from SNP leader Ian Blackford, who can be relied on to go over the top of an occasion rather than rising to it. He called on the Prime Minister to resign, and told the chamber he had nothing more to say to Johnson — only to offer a verbose point of order at the end in which he complained that the PM had left the room. He advocated Johnson being removed from office. The effect this had was to remind Tory MPs of how annoying they find Blackford, rather than intensifying their feelings of rage at their own party leader.

Others did a better job of this, including a Conservative, William Wragg, who asked icily at the end of the session why anyone would be ‘convinced by this diversionary tactic’ of Covid passports (which could be announced later today or tomorrow). Another question is why anyone would be convinced by the Prime Minister’s claim to Labour MP Catherine West that there was not another party held in the Downing Street flat on 13 November — but that all rules had been followed anyway. This is the holding line he’s been offering for the past week on the 18 December party, and which he has been forced to abandon today thanks to a leak from someone who worked for him.

It is worth remembering that this leak would not have emerged had the Prime Minister been able to tell the truth from the outset. It was only sent to a broadcaster by someone upset about the way this was being handled. Now he has thrown his own staff under a bus, he may find that others are willing to provide evidence of other parties that both didn’t take place and magically obeyed the rules at the same time.