The Supreme Court’s decision that Parliament must trigger Article 50 and fire the starting gun on the process for leaving the European Union should have come as a surprise to nobody.

Nevertheless, by putting the decision firmly in the hands of MPs, it shines a light on a deep split in the Labour Party. Most of us campaigned to keep Britain in the EU and there is a groundswell of opinion from many MPs and members that we should ‘stick to our principles when the government brings a bill to the Commons and vote against it – to ‘block Brexit’ in alliance with other parties and a few Tory rebels.

I understand that desire, emotionally. Few of us wanted Brexit and many of us pounded pavements during the referendum campaign in an effort to prevent it. My constituency voted Remain, as did the surrounding ones. That effort was ultimately doomed, however – and that really is the point. We lost. We’re leaving. To throw up roadblocks in the path of Brexit now is not the answer for Labour.

If nothing else, the idea that we should only respect the results of votes where we agree with the outcome – where we win, in other words – is reminiscent of the worst instincts of Donald Trump. Of course, when you lose a vote, you are entitled to go on making the argument to try and convince people to vote differently next time – but to refuse to trigger Article 50 in the wake of the referendum result is not analogous to losing a general election and then fighting the next one.

Instead, it is akin to losing an election and refusing to step down to let the new government take office. People voted, one side won and as democrats we should act accordingly. Labour can oppose the government’s plan for Brexit, seek to amend the Article 50 Bill to ensure proper Parliamentary scrutiny and hold the executive to account on how we leave the EU – but to simply vote down legislation designed to enact the result of a referendum, the largest vote in this country’s history, is high-handed and anti-democratic.

Even if you disagree with me about the principle at play here, from a purely practical, political perspective, there is no way out of this for Labour. Let’s war-game this. If the PLP were to be whipped to vote, when the Article 50 Bill came to Third Reading in a few weeks’ time, against the bill – joined by the SNP, Lib Dems, SDLP, Caroline Lucas and enough Tory rebels to defeat the Government… would that be it?

Would we expect Theresa May to throw up her hands, admit defeat and cave in to a parliamentary majority? Unlikely. In the face of a majority vote in the Commons against even opening negotiations, the far more likely scenario is that the Prime Minister would move to repeal the Fixed-Term Parliaments Act and call for a snap election – quite reasonably, May would tell the country, ‘I have tried to deliver on the instruction the British people gave us, but this Parliament is blocking the will of the people.’

Labour would have to vote to dissolve Parliament early and go to the country – how could we not? What little credibility we are clinging to at this moment in time would be lost in a moment if we didn’t. No opposition can turn down an opportunity to put its case to the electorate. So then we’d be faced with an early election in May or June.

Now, do we expect that the number of Labour MPs, in an election called this spring framed exclusively around Brexit – a Brexit the country voted for and we had just blocked – would go up? Or do we expect it would go down?

It would be a massacre. A catastrophe. Scores and scores of good Labour MPs would lose their seats – not just in ‘Leave-voting’ seats but across the country. What’s more, they’d be replaced by hard-right Tory Brexiteers and, in some cases, by UKIP. A recent Fabian report suggested that, at a snap election, Labour could be reduced to 150 MPs – and perhaps fewer still. A broken, rump party clustered around London and a few other inner-city seats, wiped off the map everywhere else. The leadership would go and we would turn inwards, again, distracted by another bout of finger-pointing and bloodletting.

When that parliament – with scores more Tory MPs and maybe a dozen or more UKIP MPs – returned to Westminster, it would vote to trigger Article 50 after all and we would be on our way out of the EU. We would have gained nothing. Only this time, without any meaningful prospect of a marshalled opposition from a broken and demoralised Labour, and faced with the swelled, massed ranks of her own backbenchers and a vocal UKIP group, Theresa May would be pushed further to the right, towards the kind of harsh, ‘clean Brexit’ her own right flank is calling for.

Voting down Article 50 would be the recipe for the hardest of hard Brexits – and it wouldn’t stop there. Emboldened by a thumping victory and a large majority, the Tories would come for everything else we hold dear. They’d come for workers’ rights. They’d come for trade unions. They’d come for public services. They’d come for affordable housing. They’d come for the environment. They’d come for financial regulation. They’d come for foreign aid. And they’d come for the NHS – and Labour would be powerless to stop them.

In politics, you choose your battles. You choose which hill to die on. The worst of all worlds is to take to the field for a battle you cannot win – and in losing, guarantee that you’ll be crippled, unable to fight another day.

Perhaps in time, when the outcome of the negotiations is known, there may be an opportunity for people to think again – a new vote on the final terms. Perhaps there won’t. But this fight is not one that Labour can win.

We lost the vote – to vote down the bill would be wrong on principle and politically disastrous. To advocate it is madness.