Here comes the Boris Johnson Brexit wrecking ball. How could he resist a chance to ride back in to sabotage any agreement Rishi Sunak reaches with the EU? The walrus breaks the surface to warn that abandoning his treaty-breaking protocol deal is “a great mistake”, summoning old supporters – who brag that they number 100 – to his battle flag. Out comes Sir James Duddridge, ex-Brexit minister, to declare that any role for the European court of justice would be a “wedge”, knowing the issue is a deal-breaker. The European Research Group’s David Jones absurdly claims the protocol means “a foreign government governing part of our country”. In case Johnson returns, fence-sitters keep their options open, so Penny Mordaunt calls his intervention “not entirely unhelpful”. But it is. He has no scruples about stirring up the DUP to resist a settlement. With its Stormont leadership lost and a threat on its right flank, returning to the Northern Ireland assembly to play second fiddle to Sinn Féin may look less appealing to the DUP than joining a Johnson resistance. In his Brexit campaign Johnson never cared about Northern Ireland, but like Enoch Powell before him, he may find Ulster unionism a useful weapon for Conservative outcasts, and damn the lethal consequences. If a resurrection of the disgraced leader they ousted looks implausible, we know anything is possible from this Conservative generation, since they have previously inflicted austerity, Brexit, Johnson and Liz Truss on the country. Expect them to panic if a routing in council elections looks like foreshadowing a general election massacre. If the privileges committee decides he lied to parliament, and if parliament votes for a 10-day suspension, and if 10% of Uxbridge voters sign a petition for a byelection and if they eject him, that might finally nail shut his political coffin. That’s a lot of “ifs” that will be required, since Johnson is a lot more popular than Rishi Sunak among party members. And if Labour is still 22 percentage points ahead in May? Well, we already know the Tories won’t hesitate to put a scoundrel into No 10. Johnson’s shameless reign seems to have opened the way for greater public dishonesty. Evidence from scrupulous and impartial checkers at Full Fact suggests lying in parliament has become more commonplace. When errors or deliberate untruths are pointed out, shockingly few ministers or MPs correct the record or even acknowledge the complaint. Silence is their usual response. (Full Fact says newspapers are more likely to correct errors.) Who polices parliamentary honesty? Only MPs themselves, not the Speaker, which is why Johnson’s fate stays in the hands of a Tory-dominated House, just as it’s their own rule that bars calling an “honourable” member a “liar” on pain of suspension: it would be bandied about too often. Sunak may rue promising “integrity, professionalism and accountability”, as he falls into Johnsonian habits. For example, at prime minister’s questions earlier this month he threw out a bizarre accusation that the Labour party and Keir Starmer were “bankrolled” by Just Stop Oil. Full Fact, after thorough research, concludes: “We can find no evidence that this is true,” demanding, as it always does, that “he either backs up his claim with evidence, or admits his mistake and corrects the record”. Will Moy, the head of Full Fact, says No 10 failed to respond at all, so he calls on people to sign a demand that he does. Sunak also failed to correct a claim that a “record” number of new homes had been built last year: it was fewer than the year before and way off the record. It’s easy to misspeak in the heat of debate – and very easy to correct: ministers only need send an email to Hansard but they rarely do. Inexplicably, that route isn’t available to ordinary MPs, though they can correct themselves on Twitter. Johnson was a serial offender: he repeated 10 times that more people were in work than they had been before the pandemic, even after being reprimanded by the Commons’ Liaison Committee: in fact, there were more than half a million fewer. He said Starmer had voted 48 times to overturn Brexit: not true. He said the warm home discount was worth £140 a week: it’s only £140 for the winter, so why not correct it? Some Labour MPs also tell untruths they don’t correct, mostly the same one, repeated often, that the cost of living will rise by £2,620 per family this year, which Full Fact calls an unreliable assumption: it will rise, but by less. Michael Gove was the first to claim wildly that new post-Brexit trade deals were worth £800bn: untrue, as almost all are existing deals. Most damaging are Tory MPs’ potentially lethal claims about the risks of Covid vaccines, from Danny Kruger, Andrew Bridgen and Sir Christopher Chope. Full Fact lists 70 occasions in the last year when MPs have failed to correct their blatant untruths. Only seven made corrections in the Commons. Full Fact checks many other sources of untruth, including government press offices and charities. Journalists such as the great Tim Harford, of the BBC’s More or Less, pick up questionable figures: he called out “the spectacular bullshit” of Jeremy Hunt’s (uncorrected) claim of 11,000 excess NHS deaths at weekends. Peter Oborne’s excellent website keeps a running tally of MP untruths not just in the House, but in media appearances such as Lucy Frazer on Question Time parroting Johnson’s frequent lie that “we have 40 new hospitals”: they are a phantom. The BBC and Channel 4 have good analyses of dubious politicians’ claims in their reports. Who should police political truth? Chris Bryant, recused from chairing the privileges committee for the Johnson case, suggests the Office for National Statistics should demand a legally enforced correction from any MP using mendacious figures. Liz Saville-Roberts’ elected representatives (prohibition of deception) 10-minute rule bill would have legally forced elected officials to tell the truth. But applying the law makes hay for lawyers: Johnson’s privileges defence is costing taxpayers up to £220,000. Beyond obvious statistical lies, the veracity borderline is muddy territory between routine political hyperbole and downright untruth. There are half-truths such as Suella Braverman’s claim that Labour voted against funding more police officers three years in a row: yes, but only because the sum put forward by the government amounted to underfunding. Yet no one wants to tongue-tie the ordinary rough and tumble of political exuberance. More parliamentary turpitude is on its way with Johnson’s honours list feared to be full of rogues, chums and donors. But his worst legacy may be MPs’ realisation that nothing usually happens when they utter untruths. With public trust at a low ebb, a future Labour-dominated Commons could tighten its rules. Above all, it could create a culture change to shame those who refuse to apologise for what Winston Churchill was first to call “terminological inexactitudes”. Polly Toynbee is a Guardian columnist