It may at last be curtains for the Conservative Party. The executioner, the effervescent Boris Johnson, is even now contemplating the Brexit-shaped dilemma that will force him to choose between different courses of suicide.

Johnson won the Conservative leadership election with two-thirds of the vote, on a nearly 90 percent turnout, so he can feel confident in his mandate. But what is it a mandate for? On the face of it: deliver Brexit with a bit of celebrity panache, reunify a Tory base recently split by Farage's Brexit Party and see off Jeremy Corbyn. He would make activists, demoralised and frustrated over the last two years, feel good about themselves.

In the longer view, however, Johnson's victory is symptomatic of a deep crisis in the Conservative Party. There is no sign that he has the qualities necessary to cope with this predicament, let alone resolve a major constitutional crisis. The parliamentary arithmetic is against him. He has assured Tories that there won't be an election – thus, locking him into a situation where he has no majority. And despite some obsequious "pick me, sir" job-seeking from former enemies, Tory opposition is hardening. It's increasingly hard to see how this party can remain united.

The roots of the Tory crisis can be traced back to the Thatcher era.

When Margaret Thatcher was elected leader, it was clear that the Conservative Party was in serious trouble. Its vote was in long-term decline. Many sources of traditionalist conservatism – deference, religious sectarianism, empire – were on their way out. Thatcher shook things up by empowering an upstart layer of lone traders, nouveau-riches and middling-sized firms. They hated the post-war system and what they saw as a stitch-up between the big corporations, the big unions and the big state. She offered the restoration of "free market" capitalism, ending incomes and prices policies, subsidies, public ownership and many other features of the post-war system.

As part of this shake-up, Thatcher was fervently pro-European. The single market was a Thatcherite success story. But toward the end of her reign she began to warn against the project of European Union, which she saw as a backdoor to "state socialism".

This was a hyped up way of describing minimum labour standards and consumer safety. Pro-European Thatcherites thought she had lost it, and she was forced to resign. But many senior Tories agreed with her, as did the future founders and leaders of what would later become Ukip. So did many influential businessmen – the kinds of people who fund Tory political campaigns, attend Tory branch meetings, help select MPs and employ their constituents.

That was the beginning of a political crisis for conservatism. Rebellions over the Maastricht Treaty and a crisis over membership of the European Exchange Rate Mechanism divided and demoralised the Tories. This ended the period of Thatcherite revival, condemning the Conservative Party to 13 years of opposition.

Even when they regained office on the back of a coalition agreement in 2010, the rebellion didn't stop: it accelerated. It's worth asking why.

Photo: Jake Lewis

It is often mistakenly assumed that Brexit was a "big business" project, or an expression of "white working class" revolt. In fact, the businessmen who bankrolled the campaigns leading to Brexit were largely the owners of medium-sized local firms employing a few hundred people, or boutique financial firms, property developers or management consultancies. Think of ReidSteel in Dorset, one of the campaigning pro-Brexit businesses; financier Jeremy Hosking, a major Brexit Party donor; or Ukip donors like property developer Paul Sykes or spread-betting tycoon Stewart Wheeler.

Their allies were the lone traders, pub owners and suburban civic activists running the right's campaigns. Their outlook was defended by right-wing tabloids long attuned to the concerns of the middle-class right.

These businesses came to support politicians who thought the EU was a Soviet-style tyranny. How? Their larger competitors were integrated into European markets and could cope with the EU rules. Middling businesses didn't need these markets. To them, the rules simply consolidated the power of giant corporate predators.

That meant they had overlapping interests with those who claimed the EU was a leftist bureaucracy stifling local culture, the nation-state and real competition. This elective affinity was magnified by the financial crash, driving many businesses to the brink.

George Osborne's austerity project starting in 2010 did not inject new dynamism into the private sector as he claimed it would. Ukip funding soared to its highest ever levels. In the 2014 European elections, over a fifth of bosses of firms employing over 200 people backed Ukip. Meanwhile, backbench Tories went to war on their leadership over Europe – the parliament of 2010-2015 was until then the most rebellious in the postwar era.

The balancing act performed by every Tory leader since 1992 has been one of keeping the pro and anti-EU factions of Thatcherism united. Until the Brexit vote, this was achieved by signing up to most European treaties, while engaging in a stagey belligerence toward Europe and insisting on opt-outs. Cameron's failed attempt to "renegotiate" Britain's relationship with the EU was the last hurrah for that strategy, and became a preamble to his referendum gamble.

The attempt to perpetuate this strategy, post-Brexit, has been a catastrophic failure. It is the major reason – aside from the Corbyn surge in 2017 – why May was unable to deliver any viable Brexit deal.

Boris Johnson inherits a Conservative Party split from top to bottom. As is traditional, his victory speech promised to unite the party. But this is not a party that wants to be united. It is divided, not just by ideology, but by matters of hard interest.

So what is Johnson supposed to do? If he tries to deliver a "no deal" Brexit he will split his party and parliament will block him. If he tries to renege on Brexit, he will split his party. If he tries to string the Brexiteers along, and seek further delays, he will be incinerated in a fiery backlash.

Johnson is slick and ruthless, but he is also remarkably lazy and incompetent, with a record of bungling. Nazanin Zaghari-Ratcliffe is still in a Tehran prison for that reason. Nor is he sufficiently hard-headed or far-sighted to build the cross-party coalition he needs.