We’ve reached the moment when many Tories will no longer defend Boris Johnson

“Politics has taught me one thing,” Boris Johnson said during his visit to India, “which is you’re better off talking and focusing on the things that matter, the things that make a real difference to the electorate and not about politicians themselves.” He also said investigations into Partygate should not “go on and on and on”.

Thankfully, MPs drew a different lesson from the controversy, which eclipsed the prime minister’s visit. They realised they did need to talk about themselves – or, at least, the PM’s conduct – and rightly insisted on a Commons inquiry into whether Johnson misled parliament over Downing Street parties during lockdown.

Johnson might be dragging down the reputation of his party and cabinet ministers who must defend him. But many Tories – including some junior ministers and parliamentary aides who threatened to resign if an inquiry were delayed – realised parliament would have no credibility with the public if it ignored his repeated, misleading statements about the parties. They were also worried about their own reputations. For them, the government’s initial attempt to stall an investigation by the privileges committee had uncomfortable echoes of the Owen Paterson fiasco which sparked Johnson’s decline. (Does he ever learn from his mistakes?)

Labour’s proposal for an inquiry was a win-win for Keir Starmer, who has grown in stature this week with three statesmanlike and effective Commons performances on Partygate. If Tory MPs delayed an investigation, Labour would accuse them in their constituencies of a cover-up. If they forced Johnson to concede an inquiry – as they did, by threatening to abstain in large numbers – it would prolong the Tories’ agony until the autumn, as it now will. The shambles over Thursday’s vote added to the intense frustration of Tory backbenchers and undermined Johnson’s claim to have sharpened up his No 10 operation following criticism in Sue Gray’s initial report on Partygate.

The rebellion wasn’t just about MPs’ personal prospects. It marked the moment when many Tories were no longer prepared to defend Johnson. They are not yet ready to depose him, but this week’s events are very ominous for him. “This was a staging post on a journey; people will get there, eventually,” one former minister told me.

Enough MPs realised that parliament’s whole purpose of holding the government to account rests on ministers telling the truth. That all members are “honourable” was once taken for granted. But not under a populist PM with little respect for such traditions once he is in a hole.

MPs should now go further and insist on reforms to plug the gaps in the UK’s unwritten constitution. It doesn’t require a commission taking years or even a wholesale review. But small steps could make a big difference, by stopping Johnson or a successor ignoring the spirit of the rules. For example, Christopher Geidt, Johnson’s adviser on ministerial interests, should get the power he wants to launch investigations into the conduct of ministers, including the PM, rather than wait for the PM’s permission. This would weaken the PM’s position as judge, jury and upholder of the ministerial code, which evolved when no one could envisage the UK having a Trump-like leader.

Steve Baker, a formidable backbench organiser and Brexiteer who has now turned against Johnson, made a good point in Thursday’s debate: “If the prime minister occupied any other office of senior responsibility, if he was a secretary of state, if he was a minister of state, a parliamentary undersecretary, a permanent secretary, a director general, if he was a chief executive of a private company or a board director, he would be long gone.” But the safest bet in politics is that Boris Johnson is not going to sack himself.

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Of course, an adviser like Geidt could not have the power to remove a PM. But having the right to investigate him and to publish his findings would allow MPs to make a judgement. If a PM used his Commons majority to save his skin, it would fall to the voters to deliver their judgement.

The opinion polls suggest people have made up their minds on Partygate: three out of four think Johnson did not tell the truth. Despite that, some loyalist MPs argue privately that the controversy will have faded by the next general election, saying the 2019 scandal over MPs’ expenses had surprisingly little impact at the election a year later. They are right to think the cost of living crisis will be a bigger headache for the Tories in 2024. But elections are not single-issue events and Partygate will likely provide a damaging backdrop if Johnson is still leading his party.

I don’t think memories will fade as quickly as these Johnson allies hope. The public was not directly involved in the expenses saga, but everyone was affected (in many cases tragically) by Covid restrictions on which Johnson turned from maker to breaker. That should not be forgotten, and won’t be.