We can’t know for certain how long Boris Johnson will survive as prime minister or whether his departure is indeed, as one of his ministers whispers, “a matter of when, not if”. But there are two things we do know, because they are true right now. We saw vivid evidence of both this week. The first is that his authority is shot. The second is that his continued presence in office is already corroding and corrupting our democratic system, and that this is not a hypothetical threat awaiting us in the future. It is already here. The proof of his vanished authority came 13 minutes before MPs were due to debate a Labour motion to investigate Johnson on the gravely serious charge of deliberately misleading parliament. Johnson and his team had hoped to order Tory MPs to block it, or at least to delay it. But too many Conservatives refused to do as they were told. They didn’t fancy going into the next election with their faces on opposition leaflets, alongside a reminder that they had voted to cover up Johnson’s lies about partying during lockdown. Downing Street was late getting that message. So late that, with just minutes to go, it had to back down and let Labour have its way. This, remember, is the new, supposedly streamlined No 10 operation installed by Johnson to replace the previous crowd, who with Johnson at the helm turned the seat of government into a frat house during the first phase of the pandemic. It seems incompetence and lack of nous – starting with the most elementary political skill, namely an ability to count – have been restored to Downing Street. Remember, too, that this is a government that won an 80-seat majority a little over two years ago. Yet now it cannot rely on its own MPs to do its bidding. And so, on Thursday, it had to watch as Labour took back control. The loss of authority stretches far beyond Westminster. A YouGov poll this week found that 78% of Britons believe Johnson has lied over Partygate. Even among Tory voters, only 17% say he’s told the truth. It seems laughable to speak of “moral authority” and “Boris Johnson” in the same sentence, but it is now plain that the prime minister has none. Of course, there are some who still credit Johnson with Houdini powers of escapology. They look to next month’s local elections and suspect that Johnson’s critics have erred by prophesying a Tory wipeout. Anything less than that, and the PM will boast of his resilience in defiance of the “gloomsters”. They note, too, that the Commons investigation by the privileges committee could stretch into the autumn, buying the PM precious time. But there are plenty of Conservatives, not all of them longtime enemies of the PM, who believe that “the dial has shifted”, that the Johnson premiership is now in a state of irreversible decay. A tremor went through many with Thursday’s declaration by Steve Baker that “the gig is up”. It’s not just that Baker is a strident Brexiter: others of that affiliation have abandoned Johnson already, most notably David Davis with his “In the name of God, go” speech in January. No, what matters about Baker is not what he said, but what he might do. “He’s the most lethal organiser,” says one Commons colleague. He won’t be satisfied with a simple statement of withdrawn support for Johnson. “He’ll be installing the telephones.” Add to that the prospect of more fixed-penalty notices – with reports late Friday that a new batch of fines has started to land in Downing Street inboxes – and, as one Tory MP puts it, leaked photographs of the PM “dancing on the Downing Street photocopier”, and they remain convinced that Johnson’s removal is only a matter of time. Conservatives had been banking on there being no more fines between now and local election day. The Metropolitan police said on Thursday that, helpfully, it would announce no such sanctions until after 5 May. That rather astonishing policy may now be unravelling, but it points to the second political certainty, one that awaits no further confirmation but which is already established: that this scandal and Johnson’s refusal to leave Downing Street are corroding our system of government. In a healthy democracy, the police would investigate lockdown parties in Downing Street the same way they investigate any other crime. But that is not what has happened. As Adam Wagner, a barrister who has become a specialist on Covid rules, puts it: “Why has the schedule of this investigation been so heavily influenced by what is convenient to the government?” The pattern is striking, starting with the initial Met refusal to investigate Downing Street parties at all, a position only reversed after a legal challenge. Then came the decision not to interview those involved, instead merely presenting them with a questionnaire. “Everything they’ve done has made it look like special treatment,” Wagner tells me. To be sure, police guidance suggests officers should avoid doing anything that might “affect or influence the outcome of [an] election”, but a few pages later that same guidance makes the obvious point that “delaying an announcement could itself influence the political outcome”. The Met could have gone either way. It decided to go with the course of action most favourable to the government. The charitable reading is that all of these decisions – including the initial one, taking on trust Downing Street’s insistence that no rules had been broken, and therefore concluding no police investigation was necessary – arose because the police, in Wagner’s words, “were not prepared for a situation where the government itself was the lawbreaker”. It’s the same problem with the ministerial code, which, custom demands, is enforced by the prime minister. All of these conventions are predicated on an assumption that the PM obeys the rules and the law. None of that works when a man such as Johnson sits at the apex of our system. On the contrary, his presence there is exposing the fatal flaw in what Peter Hennessy calls the “good chaps theory of government”, the same flaw that Donald Trump revealed in the US constitution: it is not equipped for a bad chap and a party that remains loyal to him. Every day that Johnson stays, his presence contaminates essential parts of the democratic body politic, the rot spreading through our institutions. Confidence in the police will sink lower: they’ve made themselves look politically partisan. Thanks to them, faith in the even-handedness of the law is diminished. One minister wonders if civil servants are continuing to work from home in part because they are demoralised: they work for a government whose consuming purpose has become nothing more than “the survival of Boris Johnson”. We don’t need to play the Westminster guessing game about any of this. This damage has already been done. There is something rotten in the state of Britain – and its name is Boris Johnson. Jonathan Freedland is a Guardian columnist