For Labour MPs, this is the scene in the jeopardy movie when the ground begins to shake. They know that those blood-chilling tremors are the footsteps of something monstrous making its approach. The screams of the local councillors that have just been devoured by the beast are a warning to Labour parliamentary candidates that it is their turn next. The devastation to one-time Labour strongholds, from south Wales to the East Midlands to the Tees Valley, tells them to be afraid, to be very afraid. By the time we get to the final reel, we know that the casualties will be many.

There are only two people in the country still trying to sustain the fiction that the general election is competitive. One is Theresa May. “I don’t take anything for granted,” she says, with the most implausible humble-bragging. The other one playing pretendy politics is Jeremy Corbyn, who has to maintain the line that four weeks of further exposure to him, Diane Abbott and John McDonnell will miraculously change the country’s estimation of their suitability to form the next government.

After Labour had been hammered in areas of Britain that the party had controlled for decades past, he blustered that he was “closing the gap” with the Tories, before going on to claim that he was “loving every bit” of this hopelessly unbalanced fight. I dare him to say that to the faces of the hundreds of decent, loyal, hard-working Labour councillors who have just been fed into the jaws of the Tory munching machine. So deep is their anger that even where the party had a winner in Andy Burnham in the Greater Manchester mayoral contest, he refused to appear with the Labour leader.

Converting the results of the locals into the equivalent of a nationwide vote, the Conservatives have an 11-point lead over Labour. On just 27%, Labour has scored the worst result for any opposition party since the BBC started recording this metric in the early 1980s. I ought to add the caveat that the locals may not be a perfect predictor of the outcome of the general election. So here is a health warning: it could turn out even better for Mrs May on 8 June. Council elections tend to overinflate support for Labour and the Lib Dems while understating the strength of the Tories. Mr Corbyn’s subterranean popularity level was a major factor in his party’s dire performance in the locals, but he was not actually on the ballot paper as a putative prime minister in those contests as he will be when people make their choice of national government. There are Labour MPs with majorities of more than 5,000 who have abandoned all hope. I know Labour MPs with majorities in the 10,000 bracket who have become terrified that they will be consumed by the blue beast.

As an appetiser before the main feast, Tyrannosaurus Theresa banqueted on the carcass of Ukip. The plum and custard brigade lost every one of the 146 seats they were defending for the gain of just 1. Douglas Carswell has taken to describing himself as the party’s “first and last member of parliament”. I have heard some folk suggest that the annihilation of Ukip might offer solace to progressive opinion. The reverse is the case, for the electoral consequences of the Ukip implosion work massively in favour of the Conservatives. The Tories are benefiting from a reunification of the right as some of their traditional support “comes home” to the mothership. There is also plenty of evidence that many Ukip-to-Tory switchers were once Labour voters who have made a journey from red to blue via the “gateway drug” of purple. If just half of the Ukip vote at the 2015 election ends up with Mrs May in June, then that alone can put 30 to 40 Labour seats into the hands of the Conservatives.

More mortifying for Labour, there are clear signs that some of its previous support is switching straight across to the Conservatives because these voters are either pro-Brexit or anti-Corbyn. Many are both, their willingness to back Mrs May hardened by the Labour leader’s persistent and fatal failure to articulate coherent opposition to her approach to withdrawal from the EU.

The most severe haemorrhaging of the Labour vote is in some of its traditional citadels, as erstwhile working-class supporters sit on their hands or fall in behind the Tories. Robert Sharp was the leader of the Labour group on Leicestershire council until he was unseated on Thursday night. “It has been tough on the doorstep,” he lamented. “All we have had back at us is Brexit and bloody Corbyn.” He expressed with vivid pith what so many other Labour campaigners are reporting from their bruising encounters with the electorate. Many on the left like to chatter about constructing a “progressive alliance” to stop the Tories, an inherently implausible project when Labour has been captured by a hard-left leadership. It was already repellent to many moderate voters before the shadow chancellor celebrated May Day by appearing in front of a hammer-and-sickle flag. It is the Tories who have demonstrated the superior skill in assembling a power-winning alliance of voters. This now stretches way off to the right, across the middle ground and deep into what used to be solidly Labour territory.

The contradictions within such a sprawling alliance of support will catch up with Mrs May in the end, but it is amply serving her purposes for the immediate goal of winning this election. The coalition for Brexit that she has marshalled behind her is being accompanied by another realignment in Scotland, where the Conservatives are enjoying a revival by presenting themselves as the most effective opposition to the Nationalists. So we now have to regard it as a very serious prospect that Theresa May is on her way to a whopping victory. Some usually cautious psephologists are forecasting a triple-figure majority for the Tories. The last time that happened was 30 years ago. Mrs Thatcher won her 1987 landslide on the back of a booming economy. A May landslide in 2017 would be the more stunning when you consider that the Tories have already been in power for seven years and have spent that time administering a lot of austerity.

Among those already preparing for a Labour meltdown are the remaining apologists for the Labour leadership. You can tell that by the way they have used the local election losses as an opportunity to rehearse the alibis they will deploy to try to explain away defeat in the general election. Blame-shifting is already familiar from them – it is all the fault of a malevolent media and treacherous Labour MPs – but I hear a new excuse from the continuity Corbynistas. This is that the party was always going to struggle in “the circumstances”, as if the Labour leader and his comrades are not the authors of this collapse, but the victims of irresistible forces. As they begin to contemplate the impending defeat and what they will do in the aftermath, Labour people need to be clear with themselves that there was nothing “inevitable” about the disaster that has been inflicted on their party and the people it exists to help.

Mrs May is not the most awesome political genius to walk the earth. Far from it. She has little in the way of solid achievement to show for her nine months at Number 10 and has spent her election campaign swaddled in opacity about what she would do with a five-year term. Mrs May only gets to look unbeatable because of the paucity of the competition provided by a Labour leadership that combines unelectable hard leftism with utter ineptness.

It was not “inevitable” that we would have this “Brexit election” at all. This is happening because of the narrow victory for Out in the referendum last year. Only a small amount of mental energy is required to envisage an alternative history that would have produced a different result. A Labour party under more credible leadership that had demonstrated some enthusiasm for the Remain cause could very well have tipped the result the other way when the country made its choice about Europe.

When Mrs May triggered this contest, she said that she was a “reluctant” convert to the idea of a snap election. What overcame the hesitation of a politician previously renowned for an aversion to risks? Above all else, at the very top of her motives list, more important to her calculations than anything to do with Brexit, it was the state of the Labour party that emboldened her to stage this election. She would not have risked it had she thought the main party of opposition was competitive. We would not be here had she thought Jeremy Corbyn had any capacity to impede her path to an engorged Tory majority.

As Labour stares into the jaws of disaster, it is essential to grasp that there was nothing pre-ordained about this rout. The electoral evisceration of Labour wasn’t written in the stars. Defeat is not to be blamed on the whims of the gods or the tides of the moon. This calamity can’t be put down to the caprice of fate. The Tories were handed this opportunity to smash their way to a big majority because Labour made terrible choices and is under abysmal leadership.

A thumping Tory triumph now looks unstoppable. It was never inevitable.