Just as there is no greater threat to a country than patriots who claim to love it the most, so no one is more likely to impoverish the working class than those who claim to be the common people’s truest friends.

We ought by now to be familiar with the links that bind the snob to the mob and how quickly they dissolve. The decision of the investment firm Jacob Rees-Mogg co-founded to move assets into Ireland illustrates with uncanny perfection how the Brexit that the Tory right convinced “the people” to back will be all too real for the many but optional for the few.

I don’t want to pretend that other Conservative politicians are not repelled by the undeliverable promises made by the right to working-class voters. But the crisis in Labour is greater, because leaving the EU raises questions that cast doubt on its very purpose.

The Labour movement was founded to represent the interests of the organised working class. Brexit is shaping up to be the greatest disaster for working-class Britain since Thatcherism, albeit a disaster that large numbers of working-class voters wished on themselves.

Asking me to support Brexit is like asking me to punch my constituents in the face. Anna Turley, MP for Redcar

I am still enough of a Mancunian to resent the way outsiders present the north as a monoglot culture with nothing more to offer than Alan Bennett and racial prejudice. But even when you notice that its great cities – Liverpool, Leeds, Manchester and Newcastle – supported Remain, the fact remains that much of the traditional Labour heartlands in the north-east, Wales, the north-west and the Midlands voted Leave.

Brexit’s potential to wreck their fragile economies is terrifying. A government assessment concluded that the GDP of the north-east would fall by 16% after a “no-deal” Brexit, by 11% if there is what the Brexit PR men cheerily call “Canada plus” and by 3.5% if Britain leaves in name only.

“Asking me to support Brexit is like asking me to punch my constituents in the face,” said Anna Turley, the Labour MP for Redcar,which voted 66:34 to leave. “It doesn’t make it easier if you tell me my constituents want to be punched.”

A claque of rightwing voices screams that MPs have no alternative to punching their constituents in the face. Punching people in the face is the people’s will. The only choice for democratic politicians is to make a fist and thump their voters as hard as they can, draw back and then thump them again.

The leftwing case against Turley, Phil Wilson in Sedgefield, Mary Creagh in Wakefield and all the other Labour MPs in Leave constituencies who are “defying” the voters by backing a second referendum ought to be made by the Labour leadership. Until 2016, Jeremy Corbyn and John McDonnell had voted on apparently anti-capitalist grounds against British membership of the EU all their political careers. Now the time for “socialism in one country” is upon them, it would be a good to hear what those grounds are. Answer comes there none.

Labour’s leaders have delivered no speeches and published no programme on how a leftwing Brexit might work, presumably because a policy that hits the weakest regions and the poorest people hardest cannot be described as left wing. The tragedy for the Labour party – and for Britain – is at the moment when it most needed effective opposition it found itself with a far left as clueless as the Brexit right.

The opponents of Brexit in Leave seats are inspiring, because they can answer any question you throw at them

A more convincing line of leftwing thinking is represented by Caroline Flint, Ruth Smeeth, Gloria del Piero and other northern Labour MPs who say that the urbanised left does not begin to understand the anger in towns where all hope has gone. They talk about Brexit giving their constituents the chance to kick a failed system and speak of the enormous sense of betrayal that would follow its reversal.

Even if you concede that their descriptions are accurate, the questions pile up. Do they think Brexit will remove the causes of the anger? No. So where will the anger turn once we are out? They don’t know. Do they believe their constituents can avoid cuts to income and public services after Brexit? Of course not. When they say your voters have nothing left to lose, are they sure about that? No, there’s always more to lose. When they say: “We must deliver the referendum result”, does that include the catastrophe of a no deal?

I doubt Brexit would have happened if politicians’ reputations had not fallen so low. The opponents of Brexit in Leave seats are inspiring, however, because they can answer any question you throw at them. They’re under pressure to shut up and not just from their leaders, Momentum and their constituency associations. A rightwing terrorist crying “Britain first” murdered Jo Cox in the constituency next door to Mary Creagh’s. After the charmers who edit the Telegraph called the Tory rebel Anna Soubry a “mutineer”, she received death threats.

I could go on, as people always do, about Edmund Burke’s declaration that an MP owes the voters his judgment “and he betrays, instead of serving you, if he sacrifices it to your opinion”. But 18th-century exhortations from the pre-democratic age miss a lesson that does not just apply to MPs but to anyone who aspires to an intellectually honest life. The dissident MPs know that democracy is an argument that never ends. They do not regard their constituents as stuck in boxes marked “Leave” and “Remain”, but see it as their duty to try to make a case that might change minds.

At the very least they insist on this point: it is not an anti-democratic betrayal to ask voters who once said they wanted to be punched to take another show of hands just to double-check that a fist in the face remains their heart’s desire.

• Nick Cohen is an Observer columnist