The good, the mad, the dishonest and the cowardly – that’s roughly how the House of Commons split last night and probably will again tonight. The honours go to those Tory MPs and ministers – especially the four cabinet ministers – who sought to ensure that whatever else happens they will not lead the country to destruction. They can hardly be sacked since they were promised a free vote until only minutes before the division, when the prime minister tried to swerve her troops into the wrong lobby.

The no-deal horses of the apocalypse were well described by the chancellor: the introduction of appalling tariffs that would slaughter industry swamped with cheap goods while killing exporters whose goods get too expensive, as smuggled EU loot undercuts everyone via the Irish border. He couldn’t have said it plainer – but then what? He jumped on to one of those horses and galloped into the lobby to vote to allow that to happen. List him among the dishonourable.

A mix of the mad, bad and cowardly voted for the Malthouse “managed no deal” – so off-the-wall you wondered how the 164 MPs entered the lobby with a straight face. A two-year extension and then a no-deal crash-out that the EU has resoundingly rejected? Any leadership contender who voted for this preposterousness out of sheer grassroots-pleasing ambition, well aware it was nonsense on stilts, should instantly be struck off any list of plausibles – Jeremy Hunt, Sajid Javid, Gavin Williamson, Penny Mordaunt and Andrea Leadsom.

In the mad-not-bad camp are the hardcore European Research Group (ERG), the no-deal zealots who passionately believe the EU is the work of the devil and they are the nation’s saviours. How many will sacrifice themselves, we shall see. For if Theresa May’s ineptitude looks likely to cause a two-year extension or a Norway soft Brexit, they could go nuclear and bring the House down. It might only take 25 crusaders for pure Brexit to call a vote of no confidence in the tattered remnants of their government: with the gleeful agreement of all opposition parties, they could cause a general election. Would they? Or as I write, are the DUP and enough of the ERG succumbing to the revamp of Geoffrey Cox’s backstop legal advice?

On Labour’s side, the siren calls from Jeremy Corbyn and John McDonnell for “compromise” across the House are very good politics. Labour sounds sensible, moderate and practical. There will be indicative votes for a customs union, for the single market, for Norway. But come the crunch, Labour will not be able to vote for any government Brexit – it will not and cannot end up as the enabler, because all Brexits are bad. Whatever Corbyn’s private view, the iron law of oppositions is to oppose, especially when they see a government that only needs a prod to roll over dead. A few Labour MPs may be tempted to opt for a soft deal – but as waverer Lisa Nandy says, the future map beyond withdrawal would need to be spelt out in law – not the blind Brexit that the likes of Michael Gove or Boris Johnson intend to warp into the hardest regulation-free regime once the withdrawal deal is done. Labour is not – and should not be – Brexit’s saviour: ultimately, it will back a referendum.

Today Peter Kyle and Phil Wilson will hold off their amendment to pass her deal but only with a confirmatory referendum, until May staggers back with her deal a third time next week. Kyle says they need 30 Tory MPs to win it: Labour will whip in favour. The fear is that the Independent Group, self-defined by promoting a referendum, will pre-empt it with their own amendment tonight, before those Tory votes are secured – this is a bad mistake that the People’s Vote campaign are begging them not to make.

There is a bigger prize, with referendum or election possible: every day that passes, Labour misses the chance to be the opposition the country needs – the pro-European voice of reason. It’s not too late for their leaders to say, look, we have tried but see how every variety of Brexit is self-harm: remaining in the EU is the best deal, now all Brexit promises have turned to dust. We are the truth-tellers, backing a chance to let you the voters end this chaos.

There are enough wise heads among shadow ministers yearning for Labour to lead a full-throated positive European campaign. Can they?

It’s too late now for side-stepping, just hoping the Tories by themselves cause a disastrous Brexit that destroys their party for a generation, with no Labour fingerprints on the Brexit fallout. All the belief in their honesty that brought Corbyn and John McDonnell to the leadership risks being dissipated by transparent political calculation: it’s a disingenuous pretence to offer Brexit compromises. The Tory party’s broken pieces may never be reassembled. Labour risks falling apart as spectacularly if it becomes the Ramsay MacDonald enabler of the Tories’ Brexit, rescuing them. Labour will whip strongly to back the Kyle-Wilson amendment – but they must become the pro-European opposition the country needs to campaign in either a general election or a referendum.

• Polly Toynbee is a Guardian columnist