While MPs seem mesmerised by their new-found power, the rival party machines are frantically preparing behind the scenes for a snap general election. It could play out like this: Yvette Cooper’s amendment, delaying Brexit until Christmas and forbidding the no-deal option, is passed by MPs on 29 January, and Theresa May marches out into Downing Street the next day to call for a dissolution of parliament.That would, for now, take a second referendum off the table.

May’s likely strategy would be to make the election about a single issue: back my deal and restore the authority of parliament, or see chaos ensue. With alacrity, polling day could be 14 March and, if May falls, a new government could reaffirm the Cooper timetable, beginning a new round of engagement with the EU. But on what basis?

The answer to that depends entirely on a struggle that would take place within the Labour shadow cabinet, the party’s National Executive Committee and the Parliamentary Labour Party. And on whether the Tory party splits.

There are, of course, other potential outcomes but I want to wargame the election scenario for Labour. Hang onto your hats, comrades, because it’s not pretty.

Labour needs 322 seats to form a parliamentary majority. It is currently on 256 and there are five “independent” MPs who have defected from Labour. To form a majority, the party has to win back all five seats from the defectors plus 61 more seats. To form a minority government with the SNP, Plaid Cymru and the Greens, Labour would need to be the largest party, which means taking at least 31 seats from the Tories and not losing any.

Of the top 100 marginals winnable by Labour, 28 are in Scotland held by the SNP, with a largely Remain-voting electorate; and 64 are English seats held by the Tories where a majority voted Leave in 2016.

The existential fact is: you can’t win the Scottish seats if you campaign on any form of pro-Brexit strategy. In fact, according to one trade union poll analysis I have seen, Labour would lose four seats in Scotland (where it currently holds just seven) if it promised to implement Brexit.

But if you can’t win Scotland with a pro-Brexit line, the same analysis suggests, promising to renegotiate a soft Brexit would have zero positive effect for Labour in the Leave-supporting areas of England, while triggering the loss of a further 14 seats in south east England.

What strategy flows from this? First, the strategic aim for progressives has to be to split the Tory party. When Boris Johnson accused the “deep state” of seeking to sabotage Brexit in the Commons, it was a signal of how easy this could become. The language fuelled rumours of a new pro-Brexit party, consisting of Johnson and Nigel Farage, and backed by Steve Bannon and a gaggle of nationalist neoliberal cranks. If such a party stood against the Tories, it would open every one of the top 60 English marginals to a potential Labour victory.

A Tory split would cut with the grain of history. The British ruling elite is riven between those who want to run regulated businesses, in partnership with the trade unions and in a stable environment; and those who want to subject Britain to the shock doctrine of chaos, deregulation and cultural warfare. Since its capture by hard Brexiteers – a faction represented in the current cabinet by Michael Gove, Penny Mordaunt, Liam Fox and Jeremy Hunt – the Tory party has been acting materially at odds with the interests of the managerial class. That’s what Johnson meant when he exclaimed “fuck business”.

If the Tories don’t split, but go into an election promising to honour May’s deal, leaving the UK subject to European rules for an indefinite period, that will also enhance Labour’s chances. Some 57 per cent of Tory voters want a no-deal Brexit and might be persuaded to stay at home, handing Labour victory even with its own vote stuck at 38-40 per cent.

Right now, Labour’s decision makers are obsessed with the issue of a second referendum. There is strong opposition to it on parts of the Labour frontbench and among the party apparatus. The assumption is that, by backing a second referendum, in which Labour is implicitly committed to vote Remain, they expose Labour candidates in England to the charge of betraying the mandate of the first referendum.

In a snap election the dynamic is different. The whole issue revolves around whether you consider the mandate of the 2016 referendum still valid. If May’s deal is again defeated decisively in the Commons, and no other form of Brexit can be passed, I think the moral force of the 2016 referendum evaporates.

In this case, no form of Brexit acceptable to the Brexiteers is possible. The progressive majority in Britain – and support for Remain is 55 per cent and rising – has no moral duty to deliver for a bunch of xenophobes what they cannot deliver for themselves.

But if you think the moral force of the 2016 referendum binds all future governments, you are not only implicitly revising the British constitution, you are enslaving the 1.4 million young people who’ve come of voting age since 2016 to the decisions of one million others who are already dead. Put another way, you are aligning Labour strategy to an electorate that no longer exists.

So if May calls an early election, Labour should go into it promising to scrap Brexit and remain in the EU on a programme of aggressive reform. Its slogan should be: “end the Brexit chaos, let’s rebuild Britain instead.” The majority of the PLP would support this and at least 80 per cent of the membership on current polling.

Whatever the legitimate fears of Labour MPs in Leave voting areas, the fact is they’re in a minority. Their counterparts in Bristol, Norwich, Glasgow, London, Cardiff and Manchester are not going to voluntarily campaign yet again for the strategic programme of the right in British politics.

In the 2017 election Corbyn faced a slew of right-wing Labour candidates disavowing him on the doorstep, while supporting his manifesto. This time the danger would be left-wing Labour candidates openly disavowing the manifesto itself. “Vote for me and I will block any attempt to impose Brexit in this new parliament” would be a very compelling message in Labour’s metropolitan heartlands, and probably the only sensible survival strategy for its seven Scottish MPs.

In the event of a snap election, the Labour left faces a defining choice. Are we going to let the limits of our radical social democratic project be determined by a few union leaders at odds with their own members, and by a referendum whose moral force is spent? Or are we going to fight for what’s in our hearts?

If the Tories split, it is a no-brainer for Labour to fight the election on a stop Brexit manifesto, combined with an offer on the economy, climate change and democratic reform that is even more radical than in 2018. The prize, in this situation, is clear: to wipe out British conservatism as an electoral force for a generation, end the neoliberal era and democratise the UK’s institutions.

But if the Conservatives don’t split, on current numbers, the gamble for Labour is bigger. With 57 per cent of Tory members wanting a no-deal outcome, however, there is a chance that, even if Labour backed Remain, a Conservative manifesto committed to the May deal would suppress the vote enough for Labour to win.

Alternatively, Labour could say: “we’ll make a final attempt to renegotiate Brexit and then put the outcome to a second referendum”. That might be enough to create a mass tactical voting effect among Remain voters while winning the pro-Leave marginals in England.

But the aftermath would be a sorry episode: Corbyn goes to Brussels and gets the same diplomatic pasting as May. He gives Labour MPs a free vote over any deal done. It falls, through a combination of hard right and progressive opposition, and then we’re back to square one. It would be much better, as with Labour’s counterparts on the left of the US Democratic Party, to start countering the narrative of despair and xenophobia with a narrative of hope.

Corbyn is instinctively right when he says the basis for that narrative should be the shared experience of the working poor, whether in Islington or Mansfield. But the shared experience is not enough without a shared narrative. Though 71 per cent of Mansfield’s voters backed Leave in 2016, Labour lost the seat in 2017 because 8,000 Ukip voters switched to a hard-right Tory candidate.

Some 31 per cent of voters actively want a no-deal Brexit, which would collapse sterling, house prices and economic growth. No matter how much compassion and understanding we reserve for them, given the austerity and penury that are driving some towards these sentiments, the socialist thing to do is defeat them, morally and politically.

The way to do it, as Labour’s Mansfield candidate Sonya Ward is showing, is to refocus local politics on poverty, austerity, homelessness and low pay. We have to point out to the hardline no-dealers that their right-wing fantasy risks collapsing the local economy, and to the soft Brexit May supporters that their option would leave Britain a rule-taker from Europe forever.

Nobody wants to fight a culture war in Britain comparable to the one Trump’s supporters have unleashed in the US. But in working class communities, this culture war is already under way.

What we need, in the areas where Labour is up against Ukip and the Tory right, is strong language from the leadership and the candidates on defence, national security and crime, backed up with clear spending commitments. Plus, an argument that shows how Brexit itself is damaging our global status and our security. If Corbyn goes down badly on doorsteps in such seats, Labour needs a more diverse shadow cabinet in which voices from the north of England are allowed to emerge from the shadow of Corbyn himself.

The big picture is that the other side are now fighting for ideals. Labour needs to do likewise. It needs to make the ideals of hard-pressed communities in the English midlands and the north its own, giving them progressive form and aligning them to a project that – whether in or out of the EU – remains so closely aligned to Europe that it will always wind up the racists and Little Englanders.

In any snap election, Labour needs to lead the progressive majority around a clear project: to end the Brexit chaos; to remain in Europe but to reform it fundamentally; to outlaw the exploitation of migrant workers, and migrant-only hiring practices; and to rebuild Britain as a 21st century beacon of technology-driven growth, high welfare and liberal values.

A Corbyn government committed to this could be a transformative force in the current global landscape. That’s the prize.