What a shambles. What an undignified, mortifying mess British politics is in right now. Two cabinet ministers have gone in a week and the foreign secretary keeps his job only because it’s so awkward to move him. The prime minister has been embarrassed at home and abroad by the behaviour of her colleagues, all the more so because these scandals are so avoidably stupid.

Sexual and financial transgressions are shocking enough, although they happen in real life as well as in politics. But Priti Patel’s secret trip to Israel, where she meddled in the politics of one of the most sensitive regions in the world alongside a lobbyist who might conceivably help her run for leader one day? Baffling. Not since Theresa May returned from Snowdonia wanting a snap election has a holiday backfired so needlessly.

Can Theresa May and her government survive? Our writers’ verdicts | Sonia Sodha, Andrew Gimson, Steve Richards and Ellie Mae O’Hagan Read more

Boris Johnson’s seeming inability to get sensitive details right in a case as serious as that of the imprisoned British-Iranian charity worker Nazanin Zaghari-Ratcliffe, meanwhile, is potentially dangerous, and his reluctance to apologise embarrassing. These aren’t decisions with which you can agree or disagree according to political preference. They’re the kind of mistakes that competent ministers just don’t make, and help explain why the Conservative brand as a whole, not just the current leader in particular, is in trouble.

Competence is such a boring word. We instinctively warm more to someone whose heart is in the right place than to dreary managerialists. But in politics, today’s noble intent is tomorrow’s broken promise. Government without competence is one unforced error after another, a parade of limp excuses and crushing disappointments. That would be as true of a Labour or Liberal Democrat leadership that fundamentally wasn’t up to it as of a Tory one, but competence matters perhaps in a particular way to Conservatives.

May’s government is not loved, perhaps not even by those who serve in it. But Conservative administrations don’t ask to be loved, just respected. Tory voters don’t necessarily expect their governments to overflow with the milk of human kindness but they do expect one that can add up, run things efficiently and not trip over its shoelaces. For decades, the rhythm of British politics has been that the country swings left when a critical mass of voters feels the fabric of society needs mending – as it is beginning to do now, watching the NHS struggle – but swings right when it wants rigour restored or financial mess cleaned up. Briskly competent stewardship is supposed to be the Conservatives’ USP, the core of its brand, which is why Tory governments can get away for a surprisingly long time with being hated, but not with being a laughing stock.

And that is doubly true for May’s administration. She became leader because she was the only obvious grown-up left standing at a time when most of her MPs just wanted someone to sort out the mess left by David Cameron. But what’s less often noted is the way that, initially, belief in her competence held a fragile post-referendum truce together.

Facebook Twitter Pinterest ‘Theresa May became leader because she was the only obvious grown-up left standing at a time when most of her MPs just wanted someone to sort out the mess left by David Cameron.’ Photograph: Matt Cardy/Getty Images

Leavers trusted her to deliver although she hadn’t been one of them. May has suffered remarkably little backlash from a horrified 48% over the past year, chiefly because she helped ensure there was no such thing as a 48%. The Remain camp swiftly fractured into a group still furiously unreconciled to Brexit, and a substantial group who didn’t want to leave the EU either but understood they’d lost the argument, and assumed the government could finesse something reasonable out of an impossible situation. Crucially, enough of the latter assumed she’d make less of a hash of it than Jeremy Corbyn.

This spring’s general election shattered any belief in her supposedly supernatural powers. But May’s most powerful raison d’etre among Tory voters remains, quite simply, not being Corbyn. They fear him more than any Labour leader in decades – not just because of what he intends to do, but because of what they see as an unfitness for high office. Fairly or unfairly, he represents to Tory voters what Johnson does to many of their Labour counterparts – someone who shouldn’t be allowed near the levers of power in case he blows something up by accident.

Polling of voters who were tempted by Labour but didn’t vote Labour in June suggests a big reason for cold feet was precisely this doubt about competence. They liked the ideas and policies, but didn’t trust Labour not to screw up in pursuit of them. “Strong and stable” is a bitter joke now, but it was chosen as a slogan because it built on what were then May’s perceived strengths, and contrasted with her opponent’s perceived weaknesses. Swing voters didn’t have to love her, just believe she was more competent than the other lot. How many of them believe that now?

Conservatives console themselves that, despite everything, they’re still hovering around 40% in the polls; that millions of voters barely knew who Patel was and are unlikely to miss her much. But they forget those polls are so finely balanced that Labour could become the largest party on a swing of less than 2%. There are so many dominoes that could now fall at the slightest touch, seats it missed by a whisker last time.

The biggest winner from Priti Patel’s downfall is Boris Johnson | Jonathan Freedland Read more

True, there’s no obvious reason why the government would be forced into a general election any time soon, although byelections can’t be ruled out as a result of sexual harassment allegations. But the lesson of recent events is that, when competence drains away, disaster follows fast.

Why was Johnson ever made foreign secretary – hardly an obvious job for someone given to putting their foot in it? Because May felt obliged to put a Brexiter in the Foreign Office and he was the least-worst option. Why does Patel imagine she could be leader – the only obvious reason for so over-reaching herself in Israel? Because as things stand, anything’s possible; if May fell under a bus tomorrow, most Tory members would probably prefer a leaver to succeed her. Given that Andrea Leadsom reached the last two in the most recent contest, all bets as to who that might be are off. Ideological purity, not competence, is sovereign in the Conservative party now and ambition is overtaking sense. Until the reverse is true again, this won’t be the government’s last stupid mistake.

• Gaby Hinsliff is a Guardian columnist