Be clear which of the current crises in British politics matters more in the long term. This isn’t easy right now, when the prospect of a Conservative leadership contest inevitably triggers a Tory party and media frenzy. Nevertheless, Brexit is the root of the matter. That fact didn’t change after Theresa May addressed the 1922 Committee tonight, and it isn’t going to go away. The Tory succession battle is ephemeral by comparison.

It has long been obvious that May would not see the year out in Downing Street. Her announcement merely restated this more plainly, and without giving a date for her departure. The leadership battle later this summer is a direct consequence of the unresolved Brexit crisis that May has created over the past three years – but it is not in any way the solution to it.

May’s announcement does not automatically mean her deal will get through parliament, although she is gambling that it will. In last night’s indicative votes in parliament, no alternative gained the support of a majority of MPs. But May’s deal remains the stuff of problems not solutions, above all because it is so vague about the future relationship with Europe. That hasn’t changed a jot. The pro-Brexit right hopes that selecting a Brexiteer to succeed May will transform the issue in a more deregulatory and anti-EU manner. But these issues remain to be fought over, inch by inch, in a parliament where, even under May, there is no majority for such an approach. Things could easily get worse for the Tories now, not better.

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This would be especially true if Boris Johnson is vain enough to run and the party is foolish enough to choose him. Johnson would be wise to rule himself out right now, not least because he would struggle to win the almost inevitable Commons confidence vote with which his arrival in Downing Street would – and should – be challenged by Labour. May will certainly not be the last Tory leader brought down by Europe.

Europe matters most. This will still be the case for years to come. The next phase of Brexit talks will shape 2020s Britain and beyond. And Brexit mattered most today too. The complexities that exasperate so many were all on display at Westminster: a long argument over procedure, a diverse set of motions all debated at the same time; votes whose outcome is a matter of interpretation; the probability that several issues, including May’s deal, will be revisited soon; both main parties trying to paper over internal splits; government almost at a standstill; and, behind it all, the much larger and more detailed question of the eventual Brexit outcome itself.

Complex? Undoubtedly. Important? Unquestionably. Riveting? Absolutely.

It bears repeating at a time like this that the crisis is not simply May’s fault, even though the way she has mishandled Brexit is a reminder of the extent to which individuals matter in history. This crisis in fact remains what it has been since June 2017 – the product of a lethally destabilising convergence of three things: the challenge to parliamentary government caused by the 2016 referendum result, the difficulty of dealing with major issues in a hung parliament, and above all the immensity of the Brexit issue itself in resetting Britain’s national order and its place in the world. None of that is going to change under a new leader.

Brexit would have tested a Cromwell, a Lloyd George or a Thatcher, never mind a May. But parliament has responded this week, always seriously, and sometimes heroically. That was never more apparent than as the Commons took control of the Brexit agenda. MPs have used their muscle twice this week, first ripping up the parliamentary rulebook on Monday in the unavoidable task of providing the leadership that May failed to give; and second, with a 44-strong majority today, by foiling the government’s malicious attempt to derail the process at the first attempt.

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It is easy to mock these procedurally complex and politically fragile proceedings. Too much is happening under the pressure of time, and now the distraction of the Tory succession too. The serious mood may not last. It is too easy to make speeches pitting parliament against the people; too easy also to dismiss Britain’s politicians as useless (they are not). But as one Conservative MP put it this week, there will be “no abracadabra moment” in this struggle. Even on a day like today, it is vital to take the long view.

There are four main reasons for the transformation we have witnessed this week. The first is that May’s obdurate, Conservative-facing approach to Brexit hit the wall, with two defeats and the Speaker stepping in, combining to create a vacuum into which Oliver Letwin has stepped. Forty years ago, the young Letwin wrote a book called Privatising the World, with a foreword by John Redwood. Redwood has remained firmly anchored in his 1980 dogmas ever since. But Letwin has been on a journey from privatising the world to saving the country.

The second reason for this week’s remarkable events is May’s utter miscalculation of the energising effect that her “parliament against the people” broadcast would have on MPs, especially on her own side. She has brought the crisis upon herself sooner than was necessary. The third is the size, palpable patriotism and moral force of the immense march in London last weekend, which supplied the permission for wavering MPs to join Letwin’s effort. And the fourth is that the numbers were always there in parliament anyway. Though many MPs were deeply reluctant to step up in the wake of the referendum vote, they were always available to do so in an emergency, such as the one that May has created.

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Most of the votes that are making this happen are from the opposition benches. Tonight’s results had a heavy Labour dimension. But the decisive element in the new situation is the mobilisation of the one-nation Tories. Time and again in the past two years, the pro-Europeans, the modernisers and the liberals on the Tory benches have flattered to deceive, preferring to rally around May when she has been subverted and abandoned by the hard Brexiters. On Monday, these Tory centrists finally stood up in force, mustering 30 votes behind Letwin; they included three very effective middle-ranking ministers who resigned. Today, on the timetable motion, 33 of them voted against May. This change has been pivotal. They will surely rally around Amber Rudd now.

Yet the Tories are a two-nation party now. One part, the larger, is completely absorbed in itself, and in winning an internal party battle to capture the leadership and the next phase of Brexit. The other part – historically the more influential but now in relative eclipse, even after this week – is struggling with other parties to shape the country’s future by the tenuous cross-party consensus that began to emerge today.

Today’s events illuminated the immense dangers facing the Tories more than any opportunities. But May’s party is not alone in facing dangers. The country is as divided as deeply as ever by Brexit and all that it represents. We are all, not just the Tory party, drifting into a slow kind of civil war. If we are wise and fortunate – as began to happen this week – it will be resolved in parliament. If we are unwise and unfortunate – as may happen under a new Tory leader – the conflict may become much harder to reconcile.

• Martin Kettle is a Guardian columnist