Labour doesn’t have a policy on Brexit but it does have a series of objectives. The bad news is that these objectives cannot be reconciled with one another, let alone with the European Union.

The party leadership’s primary objective is to defeat the Government, all the better to strengthen the smell of decay coming from Theresa May’s administration and to force an election while the Conservatives are still suffering from a loss of confidence and internal disarray. But its secondary objective is to free a future Labour government from the confines of single-market rules and the reach of the European Court of Justice, which means that, come the crunch, its natural instinct is to vote with the Government, not against it.

The good news for the Labour leader is that he can rely on the support of at least 100 Labour MPs, predominantly drawn from what use to be called the Brownite wing, whose organisational centre is Tom Watson. They expected to rally around Yvette Cooper as the preferred candidate in the leadership election that they seemed sure would follow heavy defeat at the general election on June 8. Their objectives are to end the free movement of people but for Britain’s economic model to survive unscathed.

Of course, the two can’t be done together. The only way for Britain to “take back control” of its borders is for it to lose control: of its public finances, its currency and its seaworthiness among international lenders. Why? Because the only way you can escape the free movement of people is to escape the single market — which means a drastic break from the European Union and a damaging blow to Britain’s financial services and manufacturing industries.

These two Labour groups can be reconciled with one another as far as votes in the Commons go: they will vote to frustrate, damage and delay the Government but not, ultimately, to frustrate, damage or delay Brexit. The problem is that the latter group is simply in denial about the consequences of its votes. It’s still commonplace to hear Labour MPs talk about when Brexit is “finished”, which the Cooper-Watson group tends to take to mean as “when immigrants can’t come here but nothing much else has changed”. What they have yet to absorb is that everything will change, that a drastic Brexit, if it is carried out, will become the consuming project for the political lifetime of every MP currently in the Commons and very probably the generation that comes afterwards, too.

Nevertheless, for the moment, both sides can unify around meaningless platitudes such as a “jobs-first Brexit” or a deal that secures “the full benefits” of single-market membership, despite the fact that most of the MPs uttering these banalities privately believe the only way to have a “jobs-first Brexit” is not to have one, and that the only way to retain the benefits of single-market membership is to retain single-market membership. Their pact with Corbyn has the added benefit of heading off any attempts to remove Labour MPs for being insufficiently loyal to the leader.

The difficulty is that this line disintegrates pretty quickly once it comes under any kind of scrutiny. That’s why Rebecca Long-Bailey, the shadow business secretary, came unstuck on TV under questioning from Andrew Neil, eventually declaring that Labour’s policy was to “have our cake and eat it too”, the much-derided and now essentially discredited aim of Boris Johnson, the Foreign Secretary.

Long-Bailey has the misfortune to have been talked up by Corbyn’s allies as a possible future leader, which means that every mistake she makes is pored over by future rivals and the press — an unlovely fate for a political veteran, and even more so for someone who has only been in Parliament for only years.

The difficult truth is that Labour’s official line on Brexit sounds stupid because it is stupid Stephen Bush

But the difficult truth is that Labour’s official line on Brexit sounds stupid because it is stupid, not because the person parroting it is a relative neophyte. The only people who support it who have an understanding of how drastic a breach Brexit is are Corbyn’s inner circle, who see it as an opportunity for a still more radical policy platform than the one they promised in June.

The other group in Labour to understand the true scale of Brexit are the party’s shattered pro-Europeans. Largely, but not exclusively, drawn from Labour’s Blairite tendency, these MPs believe a drastic Brexit will mean that even when Labour is in office, it will be the country’s overseas creditors who will be in power. They hope, too, that their pro-Europeanism will both protect them from attempts to remove them by MPs more closely attuned to the leadership and allow them a path back to control of the Labour Party.

Their difficulty is that they don’t have a leader, at least not in Parliament. Chuka Umunna would have struggled to secure the support of all the pro-Remain Blairites if he had run for the leadership for a second time, and his amendment to retain single-market membership similarly failed to pull in the support of Labour’s entire pro-Remain tendency. (It also had the dubious distinction of being the first amendment I have covered in which the majority of those who voted for it believed it to be wrong-headed, badly timed and doomed from the start.)

Many of them might agree with Tony Blair’s warning that Brexit followed by a radical Left-wing government would be a “one-two punch” that leaves Britain flat on the canvas, but that message will hardly encourage more Left-wing Remainers to vote with them in the Commons.

So lacking either a clue or a leader, on Brexit, as with everything else, Labour MPs find themselves following the Corbyn plan, in part out of a lack of a compelling alternative and in part out of fear of what will happen to them if they don’t.