Any Labour leader would have problems managing the party’s response to the EU withdrawal Bill, Diane Abbott, the shadow Home Secretary, said today. She is absolutely right. The party has a structural fault. It supported staying in the EU, but when the people voted in the referendum to leave, it divided between those who accepted the result and those who want to fight it.

Hence the resignations from Labour’s front bench as the vote on the Bill approaches. Jo Stevens, the MP for Cardiff Central, quit the shadow Cabinet today; Tulip Siddiq, the MP for Hampstead, resigned as a shadow junior minister yesterday. Their departures have little to do with Corbyn’s leadership and a lot to do with the new dividing line of British politics.

Since the 1950s, Labour and the Conservatives have taken it in turn to be divided over Europe. First it was Labour, then, since the middle of Margaret Thatcher’s time, it was the Tories who were torn. Suddenly, on 24 June last year, the Tories snapped together, united (apart from Kenneth Clarke) behind Brexit.

At the same time, Labour split. Jeremy Corbyn was on TV at 7.30am saying: “We must respect that result and Article 50 has to be invoked now.” Many in his party were horrified. They reacted viscerally rather than rationally, and launched a doomed challenge to his leadership behind a candidate, Owen Smith, who advocated a second referendum.

Corbyn admits to three line whip ahead of Article 50 vote

Curiously, that leadership election concealed rather than exposed Labour’s division, because it was fought mostly on the proposition that Corbyn lacks any of the qualities of leadership required by a functioning opposition. This may be true but it was irrelevant while large numbers of Corbyn supporters felt he had not been given a fair chance to fail.

But the division is deep and irreconcilable. It is not between Corbynites and non-Corbynites. After all, among Labour MPs there are hardly any Corbynites. Yet Corbyn finds himself on the side of the majority of the parliamentary party on the question of Brexit.

That is because the breach has divided all factions in the party: Blairites, Corbynites and the group in the middle whom the Corbynites call Blairites but whom the Blairites blame for paving the way for Corbyn: the Brownites, Ed Miliband supporters and assorted fellow-travellers.

Thus Siddiq, who resigned from the Labour front bench yesterday, is one of the MPs who nominated Corbyn. As is Clive Lewis, the MP for Norwich South who argued in shadow Cabinet against imposing a three-line whip but who didn’t resign yesterday.

On the other hand Jo Stevens, who resigned from the shadow Cabinet this afternoon, is not a Corbynite. She supported Andy Burnham and Owen Smith in the last two leadership contests.

I don’t know if she is a Blairite as such, but the Blairites-as-such are divided too. Tony Blair himself is the arch proponent of the second referendum position – although he phrases it carefully, as a matter of keeping options open. Many of the MPs who intend to vote against triggering Article 50 are identifiable Blairites, such as Ben Bradshaw, the MP for Exeter.

Many other Blairites, however, accept the referendum as an instruction to get on with it. In most cases this follows their long-standing belief that the free movement of people in the EU should be curtailed. Thus Liz Kendall, Emma Reynolds and Chuka Umunna accept that Britain is leaving the EU and want to move the debate on to the terms of Brexit and the kind of country Britain will be outside the EU.

The Labour split is not very equal. When MPs voted on a symbolic motion about Article 50 last month, only 23 voted against triggering it by Theresa May’s deadline of the end of March. Seven times as many, 150, voted in favour – one of them, incidentally, was Jo Stevens. That means 56 didn’t vote, but even if most of them vote against the Bill next week, plus a few switchers such as Stevens, there would be a two-to-one majority among Labour MPs for “getting on with it”.

No doubt Corbyn could have managed the politics better. As Philip Collins, an actual Blairite, argues in The Times today, an effective leader would “change the subject as often as possible. Talk about the NHS, education and productivity.”