That is the end of Jeremy Corbyn, then. He will give a speech later today explaining how defeat means victory, and that holding a seat that has always been Labour means he is on the way to forming a government in three years’ time, but not even his supporters will believe him.

To be fair, they never thought he was likely to lead Labour to victory in a general election, but they wanted an authentic socialist as leader because they hoped he might inspire some kind of rallying of the left. It has turned out to be rout instead.

It turns out that you cannot run a party with an anti-nuclear leader in a constituency that depends on the nuclear industry for jobs. And in Stoke, also known as Low-Turnout Central, a constituency that provides a laboratory test of Corbyn’s strategy of mobilising non-voters, turnout dropped and the Labour share of the reduced vote also fell. Gareth Snell, the Labour candidate, managed to improve on his predecessor’s record of being elected on the smallest proportion of the electorate by being elected with an even smaller share.

Conservatives take Copeland in humiliating blow to Labour

Indeed, all those siren Labour voices wailing for electoral reform and a “progressive alliance” will have noted that Snell won a mere 37 per cent of the vote while Ukip and the Tories between them won nearly half the vote.

It was notable that the Conservative share of the vote increased in both by-elections, the reverse of the pattern in the three previous contested by-elections since the EU referendum. One of those, Richmond Park, was lost to the Liberal Democrats. Copeland is a remarkable mirror-image of that defeat, and a confirmation of the way that Brexit is redrawing British politics. In southern constituencies that voted Remain, the Conservatives are vulnerable; in the Leave north they can even win seats from the main opposition.

The precedents for such an event have been endlessly rehearsed. The last time the government party gained a seat in a by-election was in 1982, and that was in the special situation of the SDP breakaway from Labour. You could go further back, to 1960, to find a less complicated comparison. Or you could simply observe that the state of the Labour Party is now about as desperate as it was under Michael Foot’s leadership, after the Falklands war, and before Margaret Thatcher’s landslide victory in 1983.

Labour’s position is so bad that not even the NHS can allow it to hold the ground it held, let alone advance. “Babies will die” was the headline on Labour leaflets in Copeland, campaigning against the downgrading of a maternity unit in the constituency. But the Prime Minister did not even have to guarantee the future of the unit for the Tory candidate, Trudy Harrison, to overturn Labour’s small but hardly wafer-thin majority. It told us something that Theresa May visited Copeland in the final week and that Jeremy Corbyn didn’t.

Of course, Labour’s problems are deeper than Corbyn’s leadership. Brexit would have divided the party even – perhaps especially – if it had been led by someone who sincerely opposed it. But it must now be obvious to the 313,000 party members and supporters who re-elected Corbyn just five months ago that his leadership is unsustainable. What is less obvious is the answer to the question that got Corbyn to the leadership in the first place: who would be a better choice?

Finally, it is worth marking the passing of Ukip. It too is suffering from deeper, Brexit-related problems than the weaknesses of its leader, Paul Nuttall, who was the candidate in Stoke. But his humiliation there does suggest that the party cannot win anywhere. No doubt its one MP, Douglas Carswell, will return to the Conservative Party soon enough and Nigel Farage can retire to the TV studios claiming to have changed Britain for good without ever having been elected to anything in Britain.

Stoke-on-Trent Central

Lab Gareth Snell 7,853 37.1% -2.2

UKIP Paul Nuttall 5,233 24.7% +2.1

Con Jack Brereton 5,154 24.4% +1.8

Lib Dem Zulfiqar Ali 2,083 9.8% +5.7

Green Adam Colclough 294 1.4% -2.2

Turnout 38%

Copeland

Con Trudy Harrison 13,748 44.3% +8.5

Lab Gillian Troughton 11,601 37.3% -4.9

Lib Dem Rebecca Hanson 2,252 7.3% +3.8

UKIP Fiona Mills 2,025 6.5% -9.0

Ind Michael Guest 811 2.6% +2.6

Green Jack Lenox 515 1.7% -1.3