The eclipse of the Labour Party by must now be reckoned more likely than not. Future historians will look back on the years between 1924 and 2017 as the Labour era, the period when a trade union-based party was one of the big two. But, like the Whigs and the Liberals before them, the People’s Party now face being displaced as the main force on the Centre-Left.

That’s not to say that Labour will disappear completely. There is still a Liberal Party, representing those who rejected the 1988 merger with the SDP, clinging on in parts of Liverpool. There is even, incredibly, a continuity SDP, created by refuseniks on the other side, with a handful of members in East Yorkshire. Something calling itself the Labour Party will be with us for a while yet. But the party’s life force is ebbing.

Think about it. All the indications are that, however badly he does, Jeremy Corbyn will refuse to step aside, making a schism inevitable. Even if he is somehow eased out, the electorate that chose him will remain in place. And that electorate – the mass of Momentum agitators – could not have made clearer that it does not care about winning general elections. Even as Labour slides in the polls, its activists remain focused on purging Blairites. 

From the outside, Labour’s behaviour seems almost suicidal. But that’s because we’re not looking at the personal incentives of the various actors. Just as Richard Dawkins showed that apparently self-destructive behaviour in animals can be understood once we grasp that the gene, rather than the organism, is the unit of selection, so we need to identify the motives of the individuals who make up the Labour Party.

Corbyn is, as it were, the ultimate selfish gene, content to allow the host organism to perish for his benefit. His supporters don’t regard 28 per cent support in the polls as calamitous. They regard it as a vast improvement on the one or two per cent that has until now been the ceiling for Trotskyist parties. They have never been especially interested in Parliament, which their doctrines teach them to regard as a bourgeois institution. As they see it, the revolution is advancing through an essentially extra-parliamentary movement that just happens to have some MPs attached.

The motives of those MPs could not be more different. First, and most obviously, they want to keep their jobs. That doesn’t just mean holding their seats next month; it also means avoiding deselection at the hands of Momentum when the new constituency boundaries kick in. 

The longer I have spent in politics, the more I have realised that the lobby correspondents’ view of the world is more accurate than the leader writers’. Preferment, sadly, almost always trumps principle. What was it that led to the formation of the SDP in 1981? Not, as high-minded historians claim, differences over unilateralism or the EEC, but incumbent Labour MPs’ fear that they would be subjected to mandatory reselection. Exactly the same fear will almost certainly cause a split after polling day.

So much for Labour activists and Labour MPs. What of Labour voters? Let’s apply the same Freakonomicsprinciple (or, as we might more pretentiously say, the same Namierite method) and ask what their incentives are. Most traditional Labour voters want what the Labour Party used to be: a party that was economically interventionist and committed to wealth redistribution, but also patriotic and hard-headed about immigration and crime. While no party exactly matches that combination, it seems clear that Theresa May’s Conservatives approximate it more closely than Jeremy Corbyn’s Labour. Many Labour voters, especially those whose habits were broken during the Brexit referendum, when they found themselves backing a campaign led by Boris Johnson and Michael Gove, will now switch.

Labour MPs, Labour activists and Labour voters now occupy three circles that barely overlap. That is what makes a split inevitable. And that is what is behind all this breathless Blairite talk about how Emmanuel Macron won, as Peter Mandelson puts it, “by leaving his party, not despite doing so”. (New Labour types have always been unusually susceptible to European fashions.)

Even if the moderates could somehow recover control of the party – with its brand, its title and, not least, its trade union links – the problem would remain. These are not friendly times for parties of the traditional Left. It is often pointed out that, of the eight men who have led Labour over the past 40 years, seven failed to win a general election. But the decline of the established Left is a Europe-wide phenomenon. The French Socialists came fifth in the recent Presidential election, with 6.4 per cent; the Dutch Labour Party seventh in the general election with 5.7 per cent. 

Parties designed for an age of mass industrialised workforces struggle for relevance when more and more of us are self-employed. Steam railways made mass movements feasible; broadband tilts the balance back from the producer to the consumer.

A new force will eventually emerge on the British Left. In this, as in any country, a chunk of the electorate is looking for a party that stands, essentially, for an activist state. But it now seems all but certain that that party won’t be Labour.

In many ways, this saddens me. I wrote here last August that Britain had been unusually lucky in the temper of its chief Leftist party. Unlike the revolutionary socialist parties on the Continent, I observed, Labour was rooted in brass bands and the temperance movement, in working men’s libraries and Nonconformist churches. On top of which, I feel for some of my Labour friends, public-spirited (if wrong-headed) parliamentarians who suddenly find themselves being howled down at party meetings by members they have never seen before. 

Still, the quicker the reconfiguration happens, and the sooner we get back to normal two-party politics, the better for everyone. We Conservatives need a decent opposition. So, Heaven knows, does Britain.