Things may be grim and getting grimmer, but let's cheer up a little. Never mind that Labour just scored the second-lowest share of the vote in its history. Forget the fact that the Tories' free-market project is backed by a titanic array of forces, and that coalition with the Lib Dems strengthens their hand even further. No: as Britain is reshaped according to the same social model as, say, California, hold on. In four years' time Labour will be back in power – possibly aware of the weakness of its position, and likely to accept a lot of what it inherits. But keep calm and carry on; cling to that famous Herbert Morrison quotation. Socialism is what a Labour government does, remember?

That would be an outrageous caricature of Labour groupthink, were it not dangerously close to the truth. In fairness to Ed Miliband, he has at least tried to alert his colleagues to their predicament, and the need for new thinking – although his thoughts still seem to be issued piecemeal, without much of a compelling account of either Labour's past, or its future. But on the whole, the party seems stubborn and self-righteous to the point of pomposity.

One recent Labour saga says a lot. Towards the end of last year, the Labour-aligned pressure group Compass announced that it was minded to change its membership rules so as to put members of other political parties on the same footing as Labour people. Work with the Greens' Caroline Lucas and some Lib Dems had been productive, and exciting. The suggested change also recognised changing times: if the coalition seemed set on a realignment of the centre-right, wasn't it time to start thinking about the broadening of the centre-left? The move was put to the vote and passed; this week, an array of senior Greens, Lucas included, will join up.

But as they have entered the room, others have stomped out. Most of the organising committee of Compass's youth wing have resigned, stating their case in a rather deadened vocabulary that will be familiar to people who spend their spare time fussing over resolutions. It was, they said, "necessary to organise in support of the politics initially espoused by Compass as members of the party, within the party, rather than through a broader structure". In this paper's Letters page, a brassed-off former member of Compass's executive committee writes that opening out is "bizarre" and, for some reason, at odds with the imperative to work for the return of a Labour government.

Meanwhile, Labour's anti-AV tendency is in full cry, warning anyone who'll listen about a system that's supposedly "complicated" and, "expensive" and "a politician's fix". In fact, what many of them cannot abide is the prospect of a politics in which Labour will have to reach out a bit, and election campaigning will no longer consist of stupidly declaring war on everyone – Tories, Lib Dems, nationalists, Greens – with equal ferocity. These are people who remember Ken Livingstone's enlightened approach to other parties as London mayor, or the early Blair era's rapprochement with Paddy Ashdown's Lib Dems, and shudder. Indeed, their antipathy to any kind of pluralism is so deep that they have managed to create their own deranged version – making common cause with David Cameron, Michael Howard's old batman Lynton Crosby, and the Taxpayers' Alliance.

In that lost world where Labour could scrape 50% of the poll and embed its ideas in society via a vast trade union membership, Labour-til-I-die politics just about worked. Now, in a world of plural identities, waning party loyalty and a resurgent right, it has to go. Put another way, if meaningful centre-left politics will inevitably annoy Rupert Murdoch, the CBI, and the forces of international capital, keeping them at bay will need a little more than a small hardcore of activists, a few hundred MPs and what remains of the Labour movement. Didn't work last time, did it?

• This article was amended on 18 March 2011. The original version was edited in such a way as to imply that "keep calm and carry on" was a quotation of Herbert Morrison's. In fact the Morrison quotation the author was referring to was "socialism is what a Labour government does". That section has now been amended to make this clear