The Conservatives have plunged Britain into a state of chaos unprecedented in the postwar era. From a party that fought the past two general elections as a bulwark of stability against the mayhem of its opponents, this must never be forgotten. The Tories are responsible for flinging Britain into a tailspin. From David Cameron for calling the referendum to resolve an internal faction fight and Tory Brexiteers for running a campaign based on bigotry and lies to Theresa May for her red lines and “no deal is better than a bad deal”. They are all in this together, to coin a phrase, and their party must never be forgiven or absolved of guilt for what happens next.

May’s worst-of-all-worlds Brexit cannot pass parliament without the support of some Labour MPs. This is a critical fact that must dictate what happens next. May is likely to win any vote of no confidence within her party, because Tory MPs not utterly drunk on delusion understand that there is no plausible successor, and that a shift in leadership will not alter the impossible parliamentary arithmetic. Her victory will be portrayed by some as a great triumph: don’t let them get away with it. A campaign of hysteria will follow to bludgeon MPs into voting for the deal, with apocalyptic warnings of what will happen if they do not, made all the more tragicomic by May’s previous claims that no deal would not be “the end of the world”. If it is voted down, the potential ensuing market chaos – and warnings of imminent national catastrophe – will be used to coerce MPs to vote it through a second time, perhaps with some presentational concessions to sweeten the surrender.

That is why pressure must be brought to bear on all MPs, but particularly on Labour’s backbenches, not to capitulate. The “meaningful vote” can be amended to not just reject May’s deal, but also no deal, too, for which there is no parliamentary majority. An urgent motion to that effect can be brought, too. If the deal is voted down the first time, then the entire government – not just May – will have forfeited its right to rule. A vote of no confidence must be brought instead. Both the government, and the parliamentary arithmetic, must be changed. Labour’s argument to the electorate would be as follows: replace May’s negotiating position with our own, and abandon the grandstanding, to get a deal that doesn’t menace jobs, living standards and the economy. Second, deal with the injustices that led so many to vote for Brexit in the first place.

It may well be that such a plan will fail. The only possible unifier for a Tory party on the brink of existential civil war is terror of a socialist government. They know Jeremy Corbyn’s party started the last election campaign on 24%, and ended with the same share of the vote as Tony Blair in 2001. They rightly know this new administration will rip up a Thatcherite order that has ruled Britain for over a generation. In that case, it may well be that a second referendum is unavoidable. People may bemoan the party’s failure to full-throatedly back that option earlier, but as the IPPR thinktank’s Tom Kibasi puts it, if Labour had committed to this already, May’s threat of “my deal or no Brexit” would have looked plausible to the Brexiteers, allowing her to get it through. That’s without considering whether Labour would haemorrhage leave voters, without whom it cannot win an election and do anything on Brexit, or indeed anything else.

Theresa May’s Brexit deal demands a free vote by MPs | Simon Jenkins Read more

Those championing a second referendum should understand it is not the simple escape button they portray it as. Leaving aside that no Conservative prime minister will ever support another referendum without instantly being dethroned, how will this parliament agree on the question? Or, indeed, how many options there are? The last referendum unleashed demons that will stalk politics and our society for a generation: the bitterness and viciousness of a second campaign will make the first seem genteel and polite by comparison. The most reactionary elements in Britain will dominate TV, radio and press coverage for weeks, and their demagogic campaign will claim that the establishment is re-running the vote until it gets the right decision. Those who think remain would triumph second time around are showing the same arrogance and entitlement that helped lose the first referendum. Before the 2016 referendum campaign began, remain had a big lead. It then lost.

Such a monstrously divisive referendum may end up being the only option left. But the focus now must be on defeating this deal and forcing a general election that offers up a new government to renegotiate with the EU (with a delay on article 50), and finally end the austerity that is the root of this country’s political and social ills. Labour MPs must be lobbied, passionately but politely, not to prop up May and her deal. This is a moment of national peril and tragedy, and it is the Tories who brought us here. It can only be truly ended when the most catastrophic British government of modern times is finally removed.

• Owen Jones is a Guardian columnist