The definition of a gaffe is when a politician accidentally tells the truth. So ruled the veteran Washington journalist Michael Kinsley, who would surely take delight in the textbook example of the form served up on Thursday by Jacob Rees-Mogg, the satirically titled minister for Brexit opportunities. On a visit to the Eurotunnel terminal at Folkestone, hi-vis gilet over his double-breasted suit, Rees-Mogg announced that the government was delaying yet again the imposition of post-Brexit border checks on imports from the EU. He asked the public to celebrate this decision, on the grounds that it would save £1bn a year and help hard-pressed consumers by avoiding an increase in the cost of imported food. Enforcing post-Brexit checks, said the minister, “would have been an act of self-harm”. You read that right. Jacob Rees-Mogg, arch-leaver and longtime loather of the EU, is now parroting lines from the remain campaign. He is admitting that implementing Brexit in full, honouring the 2016 promise to take back control of Britain’s borders, would be “an act of self-harm”. There’s plenty to attack here, starting with the nerve of hailing this move as “saving” Britons £1bn, when this was £1bn that Britons would never have had to spend at all if it hadn’t been for Brexit. Or you could share the outrage of British farmers, appalled that, thanks to Brexit, they have been left at a serious competitive disadvantage: they now face onerous and costly checks when they ship their goods across the Channel, while French, Italian or Spanish farmers face no such hassle moving their products in the other direction. Or you could worry along with the British Veterinary Association, which warns that not checking food imports leaves Britain exposed to “catastrophic” animal diseases such as African swine fever – a risk that was reduced when Britain was part of “the EU’s integrated and highly responsive surveillance systems”. Or you could join the lament of the UK Major Ports Group, whose members have spent hundreds of millions of pounds building checking facilities, which now stand unused as “bespoke white elephants”. But put all that aside for a moment and grasp the full meaning of Rees-Mogg’s admission. He and his fellow Brexiters once looked forward to these border checks, seeing them not merely as a price worth paying for leaving the EU but as a genuine benefit. Britain would at last be free to set its own food standards, superior to the EU’s. And yet now the minister admits that putting up barriers just makes food more expensive for British consumers and risks bankrupting British farmers: precisely the act of self-harm remainers always said it would be. The irony of hearing Rees-Mogg declare that “free trade is hugely advantageous to consumers” after he and his comrades pulled us out of the largest, most successful free trade bloc in the world – the European single market – would be funny if it weren’t so bitter. At a stroke, the minister for Brexit opportunities has implicitly admitted that there are none – or, at the very least, any opportunities are outweighed by costs so great they represent economic self-mutilation. In the long story of Britain’s needless, pointless departure from the EU, the Rees-Mogg admission should count as a milestone. Which is not to say the Conservatives won’t keep banging the Brexit drum, hoping it will rally the electoral coalition it summoned back in 2019. But the sound, always hollow, will now be hollower still: thanks to Rees-Mogg, the Brexiters themselves have admitted as much. This matters not just as a twist in the Brexit saga but for the life expectancy of this government. For Brexit was this government’s founding purpose. When the best that even the loudest advocates for that project can promise is a delay in its realisation, it’s clear: the drive has gone. And without such a goal, a destination to aim for, governing parties drift and become vulnerable. If the two usual determinants of an incumbent administration’s popularity are the economy and the personal standing of the leader, those now combine dangerously for the Tories. The cost of living crisis is both deep and wide, reaching into families that had previously been getting by, albeit with a struggle. It’s the mother living off a tin of soup for herself so her children can eat; it’s the parent getting the kids to change into pyjamas when they get home from school, to avoid wearing out their uniforms. But this crisis runs in parallel with Partygate, each revelation of indulgence in Downing Street affronting not only those who followed the rules and denied themselves contact with loved ones during lockdown, but all those who do not have the money to put bread on the table, let alone pay for a suitcase full of booze. This is a Marie Antoinette government, pampering itself while too many of its people go hungry. The usual alibis are no longer working. The much trumpeted vaccine rollout is increasingly offset in the public mind both by Partygate and the handling of the first phase of the pandemic: witness this week’s high court ruling that discharging people from hospitals into care homes was “irrational” and unlawful. A new poll shows a sharp decline in the number of voters ready to forgive those early decisions just because they’re glad they got the jab. Nor does law and order any longer offer its traditional comfort to Conservatives, not when new figures show overall crime has increased by 18% in the past two years, with the proportion of those charged down to just 5.8%. On almost every issue, from inflation to immigration, tax to housing and the NHS, big majorities think the government is handling things badly. Only on defence and terrorism do the Tories get positive marks. No wonder they like to hail Boris Johnson as a leader on Ukraine, though that is of limited political value: most voters surely sense that today’s Labour party would not be doing anything different. In normal circumstances, you would say this spells doom for Johnson. He lags behind Labour and Keir Starmer on the two big ones: the economy and leadership. People are far worse off than they were, and they have lost all trust in him. His government is stripped of its defining purpose, leaving it exposed to daily squalls and scandal. And yet, while the evidence is strong that voters are making the break from this government, they are not yet fully sold on the alternative. The old line says it’s governments that lose elections, rather than oppositions that win them. But changing governments is a two-stage process: first, the electorate moves away from the incumbent party; then it moves towards the challenger. Labour and Starmer have work to do on that second stage. But the first phase is well under way – and Rees-Mogg’s accidental truth revealed one reason why. Jonathan Freedland is a Guardian columnist Join Jonathan Freedland for a Guardian Live online event on 21 June, when he will talk about the story of a 19-year-old who escaped Auschwitz and helped to save more than 200,000 lives. Book here