Let us take a stroll down the shabby corridors of Conservative history: it is June 1997, and the party leadership vacated by John Major after New Labour’s landslide is being contested, in the second round of the race, by William Hague, John Redwood and Kenneth Clarke.

In a desperate bid to see off Hague, the arch-Europhile Clarke and the arch-Eurosceptic Redwood form a pact, founded on the principle that Europe will be an open issue in the party and that Tory MPs will not be bound by a strict party policy. There is much talk of a historic breakthrough, an end to the long Conservative civil war over Britain’s relationship with the EU, and a new era of internal party unity. But even those responsible for this brief alliance know it is nonsense on stilts. In his memoirs, Clarke jovially describes it as a “last desperate idea”, quickly condemned by MPs on both sides of the divide as a “Nazi-Soviet agreement”.

Since Tuesday’s votes in the Commons on Brexit, it has become increasingly orthodox to suggest that Theresa May has pulled off something potentially remarkable. The argument runs something like this: yes, the broad consensus within the Conservative party in favour of Sir Graham Brady’s amendment is a fledgling phenomenon, and one that must be tended assiduously by the PM and her allies. But – it is claimed – she can now “fake it to make it”, preserving this parliamentary holding-position for just long enough, securing just enough concessions from Brussels to replace the Irish border “backstop” with the “alternative arrangements” demanded by the Brady amendment.

With less than eight weeks to go until our scheduled departure date, the thesis concludes, she has a more than decent chance of coaxing her fractious party over the finishing line.

And this, indeed, is precisely what May said in her Sunday Telegraph article. “[T]he UK is leaving the EU,” she declared. “The clock is ticking … I’m determined to deliver Brexit, and determined to deliver on time – on 29 March 2019.”

Though the PM, very unusually, invoked Jeremy Corbyn’s support – “he also believes the potential indefinite nature of the backstop is an issue that needs to be addressed with Brussels” – she knows full well that she cannot depend on votes from Labour. This is a party committed to Britain’s continued membership of the EU customs union, rattled by poor opinion poll performance and distracted by fresh talk of a breakaway group of centre-left MPs.

Last week, therefore, she effectively encouraged her MPs to vote against a deal that she had previously said could not be amended. Her relationship with the Tory party is now entirely Faustian. Her MPs own her political soul; she now depends upon them delivering the goods.

It is true that every new horror story about the likely reality of a no-deal exit focuses Tory minds. Do they really want ownership of a social, civil and economic disaster that will make the winter of discontent look like a single pothole on a remote country lane? I understand why it is assumed that basic electoral terror might force just enough Tory MPs to hold their noses and vote for the deal. But this is why the Clarke-Redwood pact is such an instructive parable. Lord Kilmuir’s famous dictum that “loyalty is the Tories’ secret weapon”, if it were ever true, requires an indelible subclause: “except in the case of Europe”.

Kenneth Clarke and John Redwood put aside their differences over Europe with a pact in 1997. Photograph: Martin Argles/The Guardian

So many Conservative leaders before May have tried and failed to broker a lasting truce. Major was elected by the Thatcherite right, and trimmed on Europe, but was destroyed by the European exchange rate mechanism and the rows over the Maastricht treaty.

In 2004, Michael Howard went to Berlin in a spirit of newfound comity: “You are understandably sick of constant British vetoes. And shall I tell you something? So am I.” Two years later, David Cameron instructed his party to stop “banging on about Europe”. But to no avail. In 2016 he was driven from No 10 by the referendum he had felt compelled to call after an awful lot of “banging on”.

I agree with Lord Finkelstein’s observation, when he was working for Hague, that the problem with Eurosceptics is that they won’t take “yes” for an answer. On Sunday, Steve Baker, deputy chairman of the European Research Group, and one of the brokers of the so-called Malthouse compromise with Tory remainers, was already warning of “trouble ahead”.

Brexiteers, he insisted, had “grave misgivings about the whole [withdrawal] agreement”, and not only the backstop. Andrea Jenkyns posted a similar message – to the effect that “alternative arrangements” for the Irish border were not the sum total of the hardline leavers’ demands but just the first item on a long list.

The pressure cooker of the coming weeks will test to destruction the cosmetic unity achieved on Tuesday. There is simply no reason to assume that the final phase of Brexit preparation will be governed by reason, measured calculation and an outbreak of common sense.

Why? Because these are the not the dominant forces in the Tory relationship with Europe. Last week’s votes kicked the idea of a people’s vote into touch – at least for now. Which means that the choice confronting us now is between whatever new deal May can cobble together and no deal at all.

To put it starkly: if your hopes of an orderly exit from the EU truly depend upon Conservative unity, then it’s time to start stockpiling.

• Matthew d’Ancona is a Guardian columnist