Throughout his nine years in Conservative-led British cabinets, Philip Hammond was regularly compared to AA Milne’s Eeyore. But what the lugubrious former chancellor did today was almost Tiggerish. By warning that Boris Johnson’s government is set on driving through a no-deal Brexit that parliament will oppose he gave the UK’s indolent August politics a much-needed wake-up call.

In the three weeks since a hard-Brexit Tory coup put Johnson into Downing Street, politics has drifted into La-La land. An accumulated combination of long parliamentary stalemate, public weariness, an ineffectual Labour opposition, a compliant press and the well-executed strategy of the new Tory leader has made the Johnson government’s Brexit policy seem more inevitable than it actually is. By breaking cover, Hammond has provided an overdue reminder that the facts are still the facts.

Brexit recasts voter loyalties in ways that threaten the Tory reputation as the UK's most successful electoral force

Hammond’s argument, set out in a Times article and a Today programme interview, boils down to five big points. First, the hit to the economy from no deal will be both immediate and enduring. Second, no deal risks hastening the break-up of the United Kingdom. Third, voters were not offered no deal in 2016 and did not vote for it. Fourth, Johnson’s demand to scrap the Irish backstop is a wrecking tactic designed to hasten a no-deal outcome. Finally, a sovereign parliament can, should and will stop no deal.

None of this is new. But it has rarely been stated with such cold-eyed cogency by such a senior recent Tory minister. The Brexit saga might have been rather different if Hammond had said it two years ago. The timing is nevertheless important. This is the mid-point of the summer parliamentary recess. Johnson has been impressively resetting the political agenda. But the return of parliament is getting closer. Hammond’s aim this week was to end the phoney peace.

Central to that is a last-ditch attempt to revitalise the slim possibility of a negotiated withdrawal. It remains the case that around two-thirds of Tory MPs in the House of Commons have voted three times for a negotiated withdrawal. Johnson himself still claims to want one. Hammond’s initiative confronts him with a choice. Does Johnson start talking to the EU, thereby spending some of his political capital and putting his position in his party at risk? Or does he ignore negotiations, thus maximising the number of Tory MPs who could vote him down?

It seems certain that he will do the latter, even though he will give the impression he is open to the former. He will meet Germany’s Angela Merkel and France’s Emmanuel Macron during the G7 summit on 24-26 August. He is also expected to meet the Irish taoiseach, Leo Varadkar, in early September. But Johnson is in this too deep to get out. He has set the bar very high by demanding the scrapping of the Irish backstop. That is not going to happen. It is therefore unlikely that Johnson would risk striking a compromise deal, even if one was on offer, and even if he could claim it as a victory, because he might not get it through the Commons. A leader who nonchalantly accuses his critics of “collaborating” with the EU, as Johnson did on Wednesday, does not sound like a leader looking for compromise.

This is the nation-defining battle for which Hammond has now raised his standard. It was surely not pure coincidence that today the Financial Times chimed in with an editorial that it is parliament’s duty “to prevent the British government from visiting a calamity on its own country on 31 October”. The lines are increasingly being drawn. The Speaker, John Bercow, said on Tuesday in Edinburgh that he will fight any attempt to suspend or bypass parliament “with every breath in my body”. When asked if he believed MPs could stop no deal, he replied simply: “Yes.”

Play Video 2:11 Boris Johnson answers preselected questions during first 'People's PMQs' - video

Britain now faces a high-stakes confrontation, as important as almost any in its political history, between the government and parliament over no deal. Few observers put the number of Tories who would definitely vote against the government at more than 40; the likelier number would be some way short of that. Even so, it would be the most politically consequential Tory revolt since the fall of Neville Chamberlain in 1940. Defeat for the government would certainly force Johnson to try to call a general election. But victory is soon likely to tempt him down that same path, too.

If Brexit is the most important question in British politics, the most fascinating one is: what is the political ground on which Johnson will fight the election? If Johnson’s government is thrown out by MPs this autumn, he will fight the “people versus parliament” campaign that his adviser Dominic Cummings is preparing. If he gets his way on Brexit, he will fight as the man who delivered what the nation voted for back in 2016.

Either of these contexts poses immense challenges for the Tories, however. Brexit is reshaping their party in ways unmatched since the tariff reform splits more than a century ago. But it is also recasting voter loyalties in ways that threaten the Tory reputation as the most successful electoral force in the country’s history. Until now, both major parties have equivocated about Brexit. Labour still does. But at the next election Johnson’s Tory party will be the leavers’ party, whether Brexit has been delivered or not.

This is good news for unambiguously pro-remain parties such as the Liberal Democrats and the SNP. Maybe for the Greens, too. But it offers mixed fortunes for the Tories themselves, because those losses will not be offset by the anticipated eclipse of the Brexit party. Johnson’s choice of political ground is so fascinating because he is targeting Labour leave voters at the same time as Brexit is causing Labour remain voters to embrace pro-remain opposition parties.

Johnson’s domestic political priorities should be taken more seriously. To dismiss him as an extreme rightwinger is lazy and complacent. His emphasis on law and order in the past three weeks engages with real concerns. So did his extra spending on the NHS. His focus on northern infrastructure speaks to a nascent regional strategy for neglected parts of England. One Tory strategist told me this week he would be astonished if within the next few weeks Johnson doesn’t make a speech bashing bankers and attacking the big bonus culture.

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Yes, he is spraying promises and money around. Yes, the real test will be long term. But Johnson’s instincts chime with the central message of a new report by the centre-right Onward thinktank, which argues that there has been a sea change in public attitudes away from possessive individualism towards security and a “politics of belonging”. The approach has distinct echoes of the activist governmental philosophy that marked the politics of Nick Timothy, who this week took over Johnson’s Daily Telegraph Monday column, when he worked for Theresa May.

If true, it is not just a challenge to Labour. Johnson’s domestic priorities, with their activism and big spending, are a world away from the anti-government libertarianism and economic liberalism that defined the Tory party from Margaret Thatcher to David Cameron. Johnson’s active government approach on domestic issues is anathema to cabinet ministers such as Dominic Raab, Priti Patel, Liz Truss and even Sajid Javid. Events are forcing Johnson to remake the Tory party. Whether it or he will survive the experience is on the line this autumn.

• Martin Kettle is a Guardian columnist