This election has upended British politics. A strange new landscape is revealed | Rafael Behr

Elections do not change countries overnight. They reveal changes that were hidden – or visible but neglected – beneath layers of political complacency and cultural habit. The seismic event that has delivered Labour a vast haul of seats tells of tectonic pressure that started building long before Rishi Sunak’s rain-sodden campaign launch six weeks ago, in what already feels like a distant land.

Although opinion polls made a Conservative defeat look inevitable, there is a difference between forecasting regime change and waking up in a Britain that has dispatched scores of Tory MPs to political oblivion and chosen Keir Starmer to be prime minister with a commanding majority.

To what extent the results express a positive endorsement of Labour and its leader is hard to measure. The imperative to punish the Tories for years of political malpractice was palpable on the campaign trail in a way that exultant Starmer fandom was not. But contempt for an incumbent government and enthusiasm for the only available replacement are never exactly matched. The volume of Liberal Democrat gains in some former Conservative strongholds is partly an endorsement of Ed Davey’s party, but swing voters in those constituencies knew that evicting the local Tory would help propel Starmer into Downing Street. They were happy to take that chance.

The de facto tactical voting alliance that has crushed the Conservatives to what could be their lowest level of parliamentary representation reveals a force of broadly liberal, centre-ground moderation that has been latent in British politics, but demoralised and divided.

Starmer may not have wanted to talk about Brexit during the campaign (except in defensive assertion that he will never reverse it) , but the spirit of fury that has ravaged the Tories in some of their heartlands contains a strain of remainer vengeance.

The same cultural faultline shows up in the handful of seats that Reform has won and many more where Nigel Farage’s party has pushed the Tories into third place. On terrain prepared by the 2016 leave vote, Reform has embedded itself as the natural repository for dissatisfaction with the status quo. Farage himself, finally achieving penetration of the Commons after seven failed attempts, will act as a beacon of anti-Westminster, anti-immigration, nationalist reaction. He will exploit his new parliamentary berth much as he used the platform he had as a member of the European parliament, sabotaging the institution from within, feasting on the privileges it affords him while denouncing the whole system as rotten.

Sunak’s failure to grasp that he could not compete with Faragist posturing while also trying to run a serious, credible government was the defining strategic error of his time in Downing Street.

The outgoing prime minister had the opportunity to present himself as an antidote to the reckless and cavalier style of government embodied by Boris Johnson. Rehabilitation of Conservative economic credibility might not have been feasible after Liz Truss’s calamitous short reign, but some restoration of the “integrity, professionalism and accountability” that Sunak pledged on entering No 10 should not have been beyond reach.

But it couldn’t be done with a policy agenda moulded to the whims of a hard-right Tory faction. Sunak has learned the hard way that if you offer voters a populist tribute act, they might just vote for the real thing. Whether that lesson can be absorbed by the rump of Tory MPs left in parliament is less certain. Plenty will observe the combined Reform and Conservative vote shares and imagine a path to renewal by way of merger. Resisting them will be the long-quiescent moderate Tory faction that recognises the folly of abandoning any attempt to woo back voters who find Faragism repellent.

Some of that frustration was given voice by Robert Buckland, freshly ousted from his Swindon South seat, when he urged his colleagues to end the “performance-art politics” and “stop saying stupid things”. But the best incentive against acts of wanton political stupidity should be the responsibility that comes with ministerial office. The Tories weren’t bound by that constraint when they had power, which is the main reason they find themselves banished so far from it.

To an extent, Sunak’s failure was seeded in the unstable electoral coalition that Johnson assembled in 2019 with the promise to “get Brexit done”. Implementing an agenda in government that might satisfy the divergent interests of a culturally and geographically incoherent voting bloc – the ex-Labour working-class north and the traditional Tory southern shires – was an impossible feat of political alchemy.

An equivalent challenge now falls to Starmer. The size of the Labour majority affords vast legislative power, but the sea of red on the map covers a complex disparity of interests and competing demands that the new government will struggle to satisfy. Seats that have been recaptured in what used to be called the “red wall” will not settle back into the old tribal allegiance.

The era of automatic party affiliation, handed down across generations and worn as a badge of unshakable cultural identity, is over. The dissolution of that force benefited Johnson in 2019. Now it has facilitated Starmer’s much greater triumph. But a sequence of drastic lurches from one party to another and back again suggests that volatility and shallow affiliation are the new normal.

The safe seat has become an endangered concept. Britain may have swung to Labour by a landslide, but something of the political mood and the pressures on Starmer will feel marginal.

That effect isn’t limited to the conventional Labour-Tory feud. Many of the new Starmerite MPs will have Reform as their local challenger. The Greens have built on recent council election gains to emerge as a force that can harry Labour from the left. There was a warning of underlying instability, too, in the eviction of Jonathan Ashworth from Leicester South by an independent candidate who mobilised local Muslim community anger at Labour’s position over Gaza.

With massively increased representation in parliament, the Lib Dems will want to carve out some kind of role for themselves as something other than fellow travellers and electoral accomplices to the Starmer government.

When a party has a large majority, it tends to incubate internal opposition. One of the organisational strengths of the Starmer project is meant to have been ruthlessness in selecting obedient candidates. (That appears to have backfired in Chingford and Woodford Green, where Iain Duncan Smith held his seat because the opposition vote was split between an ousted former Labour candidate, Faiza Shaheen, and her hastily installed replacement.) And the range of ferociously tough governing choices ahead – on public spending restraint, on housing, on foreign policy – could make dissidents of MPs who were vetted for loyalty.

These are relatively luxuriant problems for a new prime minister to contemplate on his first day in No 10 with a massive majority. And there are reasons to expect Starmer to manage his party and the fractious electoral tribes it represents better than Sunak could his.

For one thing, the Labour leader comes to the job with his own mandate, when the Tory he replaces wore ill-fitting, hand-me-down robes of office from Johnson, via Truss. More importantly, Starmer is not an ideologue. He is Labour to his core – the name Keir was reportedly chosen by his parents as a tribute to the party’s first leader – but the process of making his party electable again after its mauling in 2019 reveals a fierce dedication to the pragmatic ethos of what works .

Starmer will be hoping that a sustained display of competence can build actual popularity on wide but shallow electoral foundations. It is optimistic to expect gratitude from a cynical electorate that gives no benefit of the doubt to any politician, but there will be temporary leeway available to Labour for the merit of not being the Tories.

For those on the right who internalised the argument that remainers were enemies of the people and that the rule of law was a woke conspiracy against border control, it will be hard to accept that Starmer is a more authentic representative of the national mainstream than Johnson or Farage. With seats regained from the SNP in Scotland, Labour also has bolstered credentials as the foremost party of the whole United Kingdom.

The complexity of the picture beneath the headline majority doesn’t quite justify a repetition of Tony Blair’s claim to have made Labour “the political wing of the British people”. But by the simple arithmetic of parliamentary democracy, Britain has been revealed overnight to be substantially more Starmer’s country than it is Conservative.

The character of the change is not just a pendulum swing from right to left, but of political ethos. The era of Downing Street captured by ideological mania has ended. It gives way to something that should not even be remarkable but will come as a refreshing change nonetheless – the prospect, despite more volatility to come, of a government that actually governs.

• Rafael Behr is a Guardian columnist

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• This article was amended on 5 July 2024. An earlier version said that Iain Duncan Smith held his seat in Chingford and Wood Green; that should have said Chingford and Woodford Green.