There are several species of spider whose young hatch and gradually eat their own mother. The term for this macabre practice is matriphagy. This is now the fate of the Conservative party and its hungry Ukip offspring. Remainer Tory MPs are reporting sharp rises in applications to become members of their local associations – of up to 30% in the last three months. While dozens of Tory councillors defected to Ukip under David Cameron’s leadership, one report suggests at least 10% of Ukip councillors have gone the other way since 2015.

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They are unlikely to be devotees of Theresa May’s zombie premiership. The hard-right businessman Arron Banks is spearheading an effort to recruit tens of thousands of supporters of Leave.EU – an organisation that spews anti-Muslim and anti-migrant bile across social media – to the Conservatives. A party that receives more money from the dead than the living is certainly ripe for takeover. The Tory hierarchy is set to be devoured by the monsters it suckled and reared.

Let us consider how this act of political matriphagy was made possible. Cameron may have tried to reinvent himself as a husky-hugging social liberal who wanted his party to stop “banging on about Europe”, but he recognised that only a candidate burnishing their Eurosceptic credentials could hope to become leader. When he committed to leave the centre-right European EPP-ED grouping in favour of an alliance with right-wing extremists, he whetted the appetite of his party’s hard-right flank. They would always come back for more, emboldened by every concession.

Cameron talked up immigration as a problem to be dealt with while setting impossible targets that were never met, fuelling popular discontent. He announced an EU referendum at the start of 2013, hoping it would appease his backbenchers and lance the Ukip boil. But it was only afterwards that Nigel Farage’s fortified purple army surged in the polls. When Cameron’s friends Michael Gove and Boris Johnson – whose careers he had supported – used the referendum to betray him, their campaign whipped up hysteria about immigrants, further boosting the hard right. As Brexit turfed Cameron out of No 10, his party’s right believed they were the vanguard of a national revolution.

And it was May who played the decisive role. The politician who sent racist “Go home” vans around ethnically diverse communities was a natural fit for the job. She clothed herself in the garments of the populist right, sticking it to their loathed, caricatured “liberal elite”, who were now “citizens of nowhere”. Right-wing columnists favourably compared her to Enoch Powell. Tory outriders in the press portrayed dissenters and critics as traitors and saboteurs; the Daily Mail ran its infamous “Enemies of the people” front page. The paper’s political editor, James Slack, became her official spokesperson and press secretary.

Radicalised by Cameron and May, they are tired of extracting concessions: now, they must have a leader of their own

May’s strategists hungrily eyed the 4 million voters who plumped for Farageism in 2015; their mouths watering at the Labour-held constituencies whose MPs had smaller majorities than Ukip’s vote tally. By embracing Ukiperry, they calculated, the red-rosetted heartlands of the north and Midlands would tumble to the Tories. “No deal is better than a bad deal,” she declared, normalising a position of extremism. She resorted to immigration-bashing and championing grammar schools – no wonder Farage was ecstatic, noting she was “running on exactly the same ticket” and “using exactly the same words of phrases I have been using for 20 years”.

Hubris was met by nemesis: on polling day, working-age Britain decisively rejected the Tories, and their support among minority communities shrank further. But, far from humbled, a hard right nurtured by the Tory hierarchy became hungrier still. Normalised and radicalised by Cameron and May, they had grown tired of extracting concessions from weak leaders: now they must have one of their own.

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And so now the Ukip army – once derided by Cameron as “fruitcakes, loonies and closet racists” – is flooding into Conservative associations, hoping to remodel the party in its own image. Jacob Rees-Mogg may be an unlikely shout as leader, – would Tory MPs really put him on a shortlist of two to present to their membership? – but he may be the kingmaker, for a canny contender will crave his endorsement. Steve Bannon – now fashioning an international grouping of the far right – courts Rees-Mogg, Johnson and Gove. A hard right takeover is within sight.

The nation should fear the consequences: a lethal brew of bigotry, deregulation and rolling back the state beyond Thatcher’s wildest fantasies. And how have these extremists come so close to capturing the British state? The answer is as obvious as it is damning. A combination of the Tory leadership and the Tory press mothered them, just as the Republican hierarchy reared Trumpism. Before, they were too weak to do anything but piggyback. But my, haven’t they grown. And now they may well devour the Conservative party – and become Britain’s new political masters.

• Owen Jones is a Guardian columnist