If you want to understand what really motivates the Labour Party on Brexit, the best place to start is in 1974. Jim Callaghan, the newly appointed Foreign Secretary, arrived at his department and was introduced to Michael Butler, who, as the Foreign Office’s top Europe man, would have the difficult task of helping the Labour Government win a vote for “Remain” in its promised referendum on whether to stay in the European Economic Community.

“They tell me,” Callaghan said, “that you really care about Europe. Well, that’s all right, as long as you remember that I really care about the Labour Party.” And that, essentially, is still the story of Labour Party politics.

That’s easy to forget because the Labour MPs who are the loudest and most assertive are, on the whole, MPs who do genuinely care about the European Union and the United Kingdom’s place in it. There are the seven Labour MPs who publicly backed Brexit in 2016 and would do so again: three of them (Ronnie Campbell, Kelvin Hopkins and Dennis Skinner) are long-term allies of Labour leader Jeremy Corbyn, and they suspect that, secretly, his devotion to old-school Euroscepticism has never wavered.

Then there are the 80 Labour MPs who are willing to call publicly for a fresh referendum on the United Kingdom’s membership of the European Union. Both groups are willing to risk their own political careers to advance their preferred outcome to the Brexit crisis.

As a result, people often assume that the silent majority of the Parliamentary Labour Party is similarly split, but the reality is more complex. It is true that there are a large number of Labour MPs who have to keep their pro-European feelings under wraps to stay on the front bench — including, ironically enough, many of the party’s whips, who are tasked with keeping a divided parliamentary party in line.

But even if you add the silent supporters of a People’s Vote to the ones who are out and proud, you will still struggle to win the support even of a majority of Labour MPs for a referendum rerun, let alone the near-unanimity that would be required actually to get Parliament to agree to another referendum.

The problem is there are at least 100 Labour MPs who don’t like Brexit but don’t want to stop it, because they fear what will happen to them in their own, heavily pro-Leave seats if they do. This group isn’t, on the whole, that keen on Jeremy Corbyn, but they like his Brexit policy and they like even more that his popularity among party members makes it easier for them to argue against a second referendum.

One Labour MP recently grumbled to me that the only people in their constituency to have voted Remain “were in the bloody Labour Party”, but, thanks to those same members’ trust in Jeremy, their own unwillingness to back another referendum has a powerful ally.

These Labour MPs have one source of angst above all: the free movement of people within the European Union’s single market. Their anxiety about what will happen to them if they are seen to frustrate Brexit is such that the Labour leadership isn’t even certain that it can deliver enough votes to facilitate the passage of Yvette Cooper’s Bill to “take no deal off the table”, which doesn’t even stop Brexit but merely delays it for a few months to get the details right.

All of which means that anyone calling on Jeremy Corbyn to “stop Brexit” is barking up the wrong tree: the Labour leader has scarcely any more power to stop the United Kingdom leaving the European Union than you or I.

"Perhaps the only position Labour MPs can agree on is simply to say that May’s deal isn’t good enough"

Of course, from one perspective, that suits Corbyn down to the ground: he is a lifelong Eurosceptic who has opposed every European treaty to have come before the House during his time as an MP, and his preferred resolution to the Brexit crisis is that the United Kingdom leave the EU.

But the trouble for the Labour leader is that his preferred destination after Brexit is Downing Street, and he can’t get there if he has disappointed Remainers by facilitating Brexit, and he can’t get there if he has irritated Leavers by trying to block it or by promising to reverse it after an election either.

Team Corbyn has a preferred way to do this: for the United Kingdom to negotiate a relationship like that of Norway, with a customs union added on top.

John McDonnell, the shadow chancellor, and the man whose most important role day to day is preparing the ground for his leader to negotiate tricky political spots, has been meeting Labour MPs who support this outcome — as has Len McCluskey, the general secretary of the Unite union and a key power player in the party.

The problem is that a Norway-type relationship would also involve the continuing free movement of people. Its proponents talk up the ability to limit immigration from the EU but the reality is that these powers themselves are limited — their only value is in providing Labour MPs who want to be able to facilitate a close relationship with the EU after Brexit something to say to their constituents, rather than providing a meaningful policy lever.

So while a Norway-type exit might have the votes in the House of Commons, it is not certain either. So what’s left for Corbyn and for Labour? The bad news for anyone wanting to prevent no deal, let alone anyone who wants no Brexit at all, is that the safest position — and perhaps the only one that Labour MPs can agree on — is simply to say that May’s deal isn’t good enough, but never actually to agree on something in its place, so that we all go over the cliff together.