LABOUR is in the midst of a roller-coaster leadership election. Today a court ruled that the 130,000 people who have joined the party since January (most of them supporters of Jeremy Corbyn) will not be able to vote. That is a blow to the party’s far-left leader, but he will probably still win. So it remains incumbent on Labour’s MPs—who with their surgeries and door-knocking have a much better grip on political reality than their leader and his well-heeled base—to contemplate a future without him. Regular readers of this blog and my print column will know that I have long called on Labour’s MPs to contemplate ditching their leader. Yet even before today’s ruling an overwhelming majority of them strongly disagreed. Their objections go something like this. “Under First Past the Post, splitting the party’s vote would give the Tories and UKIP a clear run at 100+ Labour seats. And why should those of us who have been Labour all our lives be forced abandon it? The far left has been defeated before and it will be again. Just look at the Social Democratic Party (SDP), which by splitting off from Labour in 1981 helped keep it out of power for another 16 years; without much electoral success to show for its efforts.”

The analysis exudes reason and decency. It is also wrong. Partly because the assumption that the SDP held Labour back is unconvincing. In practice, as is often forgotten, the splinter took more votes from the Tories than it did from Labour. Moreover, it also exerted the sort of external pressure on the party’s right flank that helped the likes of Neil Kinnock make the case for change from within. And it incubated the party’s moderate tradition (Roy Jenkins, for example, came to be a mentor to Tony Blair).

And in any case, the objections are a giant category error. References to the SDP are simply otiose.

First, the Labour Party’s situation now is substantially grimmer than it was in 1981. Michael Foot was a better politician than Mr Corbyn: cleverer, more intellectually heterodox and a better speaker. In 1980 he beat Denis Healey, his moderate rival, by just 52% to 48%. Last year Mr Corbyn took 59% of the vote against three rivals—a figure on which, if nominations by local party branches are anything to go by (they usually are), he may improve in the current leadership election. Meanwhile most unions, which in the 1980s were moderate and integral to Labour’s salvation, are today in the hands of the left. And social media makes it much easier for the hard left to organise and consolidate than it was back then: Momentum is Militant with a Facebook account and a sympathetic media eco-system (think Novara, The Canary and other blinkered but popular pro-Corbyn websites, their reach amplified by the echo chambers of Twitter, Facebook and Snapchat). In this context, moderate assumptions that the reconquista can be as quick and successful as that of Mr Kinnock, John Smith and Mr Blair look wildly optimistic.

Second, the chances of a new party succeeding are better than they were in 1981. Britain is a much less deferential and rigid country than it was then. Voters are more fickle. Fewer define themselves according to the party for which they vote. UKIP's rise illustrates the electorate’s willingness to break from established parties. In other words: a new Labour breakaway need not crumble on contact with voters’ fixed loyalties as the SDP did.

Third, and most importantly: the degree of alienation of Labour’s MPs from its leadership today is almost incomparably greater than it was in the 1980s. Most of Mr Corbyn’s shadow cabinet has resigned. If he wins the leadership contest he has no chance of reconstituting a full shadow ministerial line up (if you include junior ministers). Unlike Foot he has suffered a vote of no confidence endorsed by over three-quarters of his MPs.

My point is that enough MPs despair of Mr Corbyn to split off, refound the party and annihilate its remaining, far-left rump. The problem is that the vast majority also seethe about the SDP splitters in the 1980s, see Labour as family and adore its history and tradition. That is understandable. Yet is it really truer to the party’s founding mission—to provide representation for working people—to look on as Labour systematically alienates those it was meant to serve? The most optimistic projection put to me by the anti-splitting tendency is that, perhaps, over a decade or so, Labour can be made electable once more. This is dismal. And, anyway, a more pessimistic projection is probably more realistic: that, whole, the party will simply spin off into irrelevance; Britain as a sort of delayed Poland in which a social democratic party that obtained over 40% of the vote 15 years ago shrivels into irrelevance, leaving behind a battle between liberals, conservatives and populists.

The alternative need not be as grim as those MPs imagine. If as many of them as despair about their leader quit, “Labour” will become rump of administratively incapable hard-liners, while True Labour (as we might call it) will inherit almost all of the party’s political talent. A defection on this scale would not work in the same way that the puny, 28-MP SDP one did a third of a century ago. There would follow a battle over whether “Labour” or True Labour actually owned Labour’s (1) pragmatic, social democratic heritage, (2) national voice, (3) local branches and (4) brand. If the 172 MPs who declared no confidence in Mr Corbyn in June sided with True Labour, this new party would automatically inherit (1) and (2), some of (3) and—with a successful legal challenge—most of (4). True Labour’s role would then not be to compete amicably with Mr Corbyn’s “Labour” but to marginalise or, ideally, destroy it by appropriating the Labour mantle through sheer weight, dynamism and persuasiveness. I see few reasons to believe that such a party would lack the talent, prominence, funding potential and organisational ability to do so.

Just imagine:

On September 24th 2016, Jeremy Corbyn wins reelection. Within hours he moves to consolidate his control of the party. One-by-one, MPs start declaring their independence from their reelected leader; eventually over 150 have done so. Local Labour Parties begin to split along leader-rebels lines. Staffers in Labour’s headquarters formally disregard Mr Corbyn. A True Labour declaration of independence and social democratic principles is promoted by leading MPs and Labour grandees like Mr Kinnock. A majority of Labour MPs rally around it and appoint a True Labour interim leader and shadow cabinet sporting the best of the party's parliamentary talent (perhaps: Angela Eagle as leader, Rachel Reeves as shadow chancellor, Tom Watson as a continuity deputy leader).

True Labour obtains recognition from John Bercow as the official opposition. Donors are sought and local branches established. These swallow the moderate segments of Constituency Labour Parties and welcome a flood of new centre-left and centrist members, including many previously unaligned voters politicised by the Brexit vote. The new opposition leader, Angela Eagle, discards Mr Corbyn’s unelectable stances and puts real pressure on Theresa May. Conservative splits over Europe start to fracture the government. True Labour becomes more confident and prominent as “Labour”, despite its many loyalists, sinks into chaotic infighting and—unrestrained by moderates— alights on even more looney policies. Come the 2020 election, True Labour is a competitive force, while “Labour” looks like a pressure group posing as a political party and, with few locally active door-knockers and a dysfunctional leadership, sinks into irrelevance.

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As things stand this is not a realistic scenario. But only because Labour MPs are too frit to make it a reality. Most recognise its desirability. But most are also hidebound by their tribal commitment to the “party” currently run by Jeremy Corbyn. They struggle to accept that Labour is more than its institutional carapace and that to reestablish it as a formidable electoral force is not to abandon it, but to save it and the best of its tradition. If Mr Corbyn wins the current leadership election Labour MPs must choose between two futures for their party: decades of infighting that may or may not generate an electable social democratic force or a painful but effective break that would immediately generate an electable social democratic force. The future is in their hands.