Walk the corridors of Westminster, and round every corner you encounter the pale faces of the living dead. Labour MPs look like patients who have just had the bad news from the oncologist: it’s mortal, it’s terminal, far too late now for anything more than palliative care.

Yesterday morning the Smith Institute hosted a Commons presentation by Deborah Mattinson, of Britain Thinks, and Nick Pecorelli, of The Campaign Company – leading pollsters and focus groupers who have followed Labour’s fortunes over decades. Labour politicians in the room listened to a sentence of doom most already well understand: they smell it in the air, they hear it on the doorsteps, they see it in the eyes of those who look away on the high street.

Wales! As Theresa May visited yesterday, YouGov predicts the land of Labour’s fathers and Nye Bevan is about to go mainly Tory too. One pollster says: “I still don’t think Labour have realised what a meltdown this is.” The 4 May council elections look set to be a bitter foretaste, with Labour possibly losing hundreds of seats in a vote where oppositions traditionally gain.

This malaise runs deep, as the brand of the party itself has become profoundly contaminated and mistrusted by the very people Labour thinks it’s there to support. The class and culture divide between Labour leaders and its putative voters yawns too wide to bridge.

The images of Emily Thornberry’s sneering at a white-van man’s St George’s flag, or Gordon Brown’s dismissal of Gillian Duffy as “bigoted”, have burned deep into the working-class psyche, says Mattinson. The thinking now is that Labour doesn’t like “people like us”, is neither “one of us” nor “on our side”. Whose side is it on? It’s the party of posh metropolitans who defend only immigrants and people on benefits.

The words the leadership uses have little meaning or resonance with erstwhile Labour voters. “Austerity” is empty verbiage to them, says Mattinson. Social justice, equality, fairness – these have no traction; they are abstractions that, if understood, are viewed with suspicion: more money for immigrants and people on benefits. Labour’s economic woes go back to 2008 – the party is still blamed for the crash, so any spending promises are viewed as signs of its wastefulness.

Deep dislike of Labour long pre-dates Corbyn: he’s the catalyst for catastrophe, not its underlying cause. “But leadership matters massively, more than ever before,” Mattinson says, after Labour’s three unpopular leaders in a row.

She asked her voter panels to keep diaries at the last election, and found 80% of what they wrote every day concerned their feelings about leaders, not the policies. Emmanuel Macron’s meteoric yet policy-light rise in France shows how much star-quality leadership dominates the voting. All elections boil down to a choice between steady as you go or time for a change – and right now, mid-Brexit, few voters want more change.

How bad could it be? Professor Rob Ford, a psephologist and political analyst for the BBC, warns: “You can reach a point of no return.” Even those sitting on majorities of more than 10,000 and well above are at risk. Some of Labour’s safest seats, Celtic or rust belt, have the most strongly Brexit voters, who most dislike Corbyn. It’s not impossible for Labour to fall below 100 seats, Ford says, and Mattinson agrees – though 120 might be more likely. Professor John Curtice puts it a bit higher, “but this could be the party now just of Merseyside and London”.

The Tories are trying to frighten voters with the fanciful spectre of prime minister Corbyn. Be afraid, May’s officials are briefing the FT, “We could lose our working majority” and “The Tory lead could actually be non-existent”, as they quote US election guru Nate Silver’s blog calling UK polls “terrible” and the election “riskier than it seems”.

Meanwhile, paradoxically, Labour canvassers are reassuring voters there’s not a snowball’s hope in hell that Corbyn could ever be prime minister, so it’s safe to vote for well-liked local Labour MPs. Every Labour seat needs saving in any way possible – but short of a miracle, a host of thoroughly good Labour MPs will be swept away by a sea of blue, leaving a crippled party at Westminster struggling to regain any credibility as a potential future government.

It’s not impossible for Labour to fall below 100 seats – though 120 might be more likely

This could be an apocalyptic, landscape-changing election, Ford says, like the one that swept the old Liberal party away in the 1920s. “There is no floor Labour might not fall below,” he says, as more people switch at every election.

What is the best hope for Labour MPs hanging on? Abstention was the answer of these pollsters. Old Labour voters turn against Labour, but there’s no love lost for Conservatives – especially in northern seats laid waste in the Thatcher years. Here people could still be wary of Theresa May soft-soaping them with her concern for “ordinary working families”: she talks the talk while her budget directs a programme of the deepest cuts yet to schools, the National Health Service, local councils and everything else.

Don’t give her a landslide: that may be the strongest message. It is a miserably back-foot, defeatist slogan, a minimalist plea. But the best you can hope for is that defectors from Labour will sit on their hands instead of switching to the Tories, to save Labour seats. May’s imperious dictum that “Every vote for the Conservatives will make me stronger when I negotiate for Britain” will sound threatening to many ears.

Tony Blair, that most astute political brain, urges “No blank cheque” as the best message. Don’t give her a mandate for “a Brexit at any cost driven by the ideology of the right of the Tory party”. That could rally some weak Labour Brexiters, and encourage remainer Tories to hesitate before gifting their vote to extreme hard Brexiteers. Will remainers cross tribal party boundaries to stop a hard Brexit?

As the great blue tsunami heads this way, reach for any sandbags to rescue some seats from the deluge. Tactical voting and progressive alliances can save a few. Labour looks as if it’s going down fighting over the bones of who controls the manifesto, and how many far-leftists are parachuted into vacant seats.

But what all these pollsters tell us is that we face an unprecedented swing to the right, unrestrained by effective opposition. The Brexit deal-or-no-deal that will determine the fate of the country will be signed and sealed by May long before the next election – with no vote, no election, no referendum. In the meantime, all the signs are that living standards will have slumped. By 2022 her tidal majority will feel like elective dictatorship.