Spare me the inevitable pity for Theresa May after her tearful farewell address this morning. “Oh, wasn’t she given such a terrible hand!”, people might cry, or “is it her fault that her backbenchers are such a bunch of Neanderthal extremists?”, and “it’s not her fault Brexit is such an undeliverable mess, is it?”. We must see through this. May is the worst prime minister since Lord North’s reign in the late 18th century, when the US colonies declared their independence.

May did indeed inherit a terrible hand. She then proceeded to douse it liberally with petrol and set it alight.

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Let’s start with Brexit. The official leave campaigns, and their vitriol about migrants and refugees, merely built on the foundations laid by a home secretary who sent “go home” vans around mixed communities, who spread pernicious myths of being unable to deport illegal migrants because they owned a pet cat, and under whose watch gay refugees felt obliged to film themselves having sex to avoid deportation. There is only one discernible consistency in May’s ideology – and that is bashing migrants.

When she became prime minister, May and her coterie of advisers – defined by a swagger and bravado that would swiftly become hubris – hungrily set their eyes on devouring Ukip’s voting tally in the 2015 election in order to hand the Tories the landslide victory they’d been denied for three decades. “No deal is better than a bad deal,” became her defining mantra, raising expectations to impossible levels and conferring respectability, desirability even, on a disastrous Brexit outcome: the chutzpah, then, of quoting Nicholas Winton when he said, “compromise is not a dirty word”, in her farewell speech.

Her allies in the media set about monstering her opponents, poisoning the well of political discourse: the notorious “ENEMIES OF THE PEOPLE” Daily Mail front page was penned by James Slack, who promptly became her press secretary. The May premiership will be remembered for creating an environment where terms like “traitor” and “saboteur” became commonplace. She, too, deliberately stoked a culture war that threatens to consume Britain, most notoriously in her demagogic “If you believe you are a citizen of the world, you are a citizen of nowhere,” speech. She appointed Boris Johnson as foreign secretary, antagonising the EU states with whom she needed to strike a deal and reducing Britain further to the status of a laughing stock.

For purely domestic partisan gain, she repeatedly made inflammatory speeches about the EU that achieved nothing but fostered bad will. Her chancellor, Philip Hammond, made threats that if Britain did not get what it wanted, the government would undercut the EU in a race to the bottom of tax cuts and deregulation. This was not just a commitment to repeal the hard-won rights and freedoms of the British people, but a near declaration of war on what are supposed to be Britain’s partners. But whatever her demagoguery, whatever her laughable empty platitudes of a “red, white and blue Brexit”, May had no meaningful plan at all, other than undeliverable red lines. She couldn’t negotiate a deal with her own party, let alone with 27 foreign governments.

Holding back tears, May ended her speech describing “the enormous and enduring gratitude to have had the opportunity to serve the country I love”, but her real commitment was only to her party. She promised over and over again that she would not call a general election, but believing she had the opportunity to obliterate her opposition and turn Britain into a de facto one-party state, she broke her word. Deceit and dishonesty were the hallmarks of her doomed reign. When the Tories had their majority snatched away, May became a zombie prime minister: sadly, as any avid watcher of the genre can testify, zombies can cause a lot of damage, and are very hard to dispose of.

Having hyped up “no deal is better than a bad deal”, May led Britain to the entirely predictable humiliation of a bad deal. That her party’s zealots increasingly embraced pushing Britain off the precipice was unsurprising: she kept throwing them red meat, and they had only grown fatter and hungrier.

But it’s not just Brexit, for we must judge a prime minister by her own promises. When she fatefully assumed the premiership, she declared war on the “burning injustices” she correctly identified had paved the road to Brexit. And then, in the subsequent three years, she oversaw the biggest jump in child poverty for three decades; a housing crisis which has only worsened; the rollout of a universal credit system which is a life-destroying disaster. The Grenfell fire will endure as a reminder of a social order built by Toryism which prioritises money over human life. The Windrush scandal – in which British citizens were denied medical care, kicked out of their homes and even deported from their own country – will remain a salutary lesson of where the migrant-baiting May promoted leads. The surge in violent crime will always testify to the disastrous consequences of the austerity May herself championed.

And however more insular Britain has become, let’s not forget May’s foreign policy record, either: whether it be selling weapons to Turkey’s murderous regime, or arming and backing a Saudi dictatorship that has rained British weapons on Yemen, slaughtering thousands of innocents and creating the world’s worst humanitarian disaster. If you wish to spend a moment expending valuable human sympathy, do it not for May – do it for them.

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The only leeway I will give May is this. With Britain in turmoil, it will be so easy for the Tory party to claim this is all on her; to treat her as a human sponge, soaking up all the blame. But to paraphrase George Osborne – himself one of the chief architects of the chaos of our time – they are all in this together. They all imposed cuts that ripped up our social infrastructure and fuelled discontent and anger. They all whipped up resentment against migrants for the “burning injustices” they, and their party’s wealthy bankrollers, were responsible for. They all promoted an ideology which prioritises markets ahead of human needs and aspirations.

The May era was a time of chaos; but something worse now beckons. Until Britain is rid of being ruled by a disintegrating Tory party – the proximate cause of our ills – and a rotten social order that decays further with every passing day, then the turmoil will not only continue but deepen. What a legacy to leave.

• Owen Jones is a Guardian columnist