“THE centre cannot hold,” was WB Yeats’s assertion, which we ought to take seriously, since at the same time he made the indisputable claim that “the best lack all conviction, while the worst / are full of passionate intensity”.

Before we can decide whether it’s true, though, there’s the problem of establishing what the centre is. In his excellent history of the foundation of the SDP, Claret and Chips, Hugh Stephenson made the telling point that, though the party often claimed to be “breaking the mould of British politics”, it was doing no such thing. Slightly left-of-centre social democracy had, in fact, been the policy of all post-war UK governments until the arrival of Margaret Thatcher. It was her “conviction” politics that shifted what was regarded as the political centre (and incidentally, prompted the leftward movement of the Labour party in the late 1970s, which in turn led to the SDP’s foundation).

Arguably, we have since had a sort of slightly right-of-centre market capitalism as the policy of all governments, made in part by Tony Blair’s creation of New Labour in the mould of, well, the SDP, and then David Cameron’s rebranding of the Conservatives as, well, New Labour.

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We can argue about the extent to which parties actually live up to their rhetoric: the welfare state grew under Mrs Thatcher, for example, while tax revenues fell during Gordon Brown’s premiership (though largely because of recessionary factors). But it’s the rhetoric that marks what’s usually called the Overton Window – political ideas which are currently accepted as “sensible” or “popular”, and thus stand a chance of becoming policy. Ideas characterised as “unthinkable”, “radical” or (in Yes, Minister’s damning formulation) “courageous” are outside it.

Every economist in the universe, for example, no matter how left-wing, thinks Donald Trump’s steel tariffs are a bad idea. But they are politically popular with his supporters. Similarly, Jeremy Corbyn’s plans for rail renationalisation enjoy widespread support, even though it would cost a bomb, the bit that is nationalised already is where most of the problems are, and there’s no explanation of how nationalising the rest of it would improve things. The Tories, meanwhile, have introduced all sorts of legislation, from stamp duty rises to the sugar tax, which most conservatives (with a small c) regard as profoundly unConservative.

But if every party needs a political narrative – even if its actions contradict it – what is the story with The Independent Group (a really terrible name)? When it formed on Monday night, there seemed to be a story of sorts. It was that Mr Corbyn and his supporters are unfit to govern, partly because of their readiness to condone anti-Semitism and all manner of terrorist groups, provided they are anti-Western, and partly because his economic ideas are too left-wing.

This narrative was lent extra credence by the readmission to the Labour Party the same day of Derek Hatton. So far, so SDP, which also began as a revolt by Labour MPs against Bennite dominance which rendered the party unelectable for years (coincidentally, its recovery can be dated from the moment it expelled Mr Hatton).

But then the story got confused, when three Conservative MPs (all long regarded by most rank-and-file Tory supporters as practically crypto-Communists) joined them. This, it might be thought, ought actually to help Mr Corbyn, by undermining Mrs May. The new group, after all, has one more member than the DUP, which is currently shoring up the government.

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Yet, other than their dislike of their respective parties’ positions on Brexit – which all the MPs concerned originally backed, by voting for Article 50 – it’s difficult to see what ideas the group has in common. And, if there are any, can anyone explain how they might differ from the policies of the Liberal Democrats?

There are by chance several other MPs who have become independent either by resigning from their parties or by having the whip withdrawn (or, in one case, by being in jail) who are not in this new group, and show no signs of wanting to join it. And it’s not yet clear whether the Independent Group will become a party at all.

Assuming that is their intention, however, there are several hard questions for them. And the hardest is not “What do you all believe in?” or even “How do you differ from the Lib Dems?” but “Why do so few people vote for the Lib Dems at the moment?” For this is one of the great puzzles of our time.

Given that 48 per cent of the population voted Remain, and that the LibDems are the only UK-wide party to continue to oppose Brexit, you would expect them to be storming the polls. But they’ve even managed to lose one of their 12 MPs (Stephen Lloyd, now independent, but not in the Independent Group). Unsurprisingly, Sir Vince Cable is making “come hither” eyes at the new group, but he must also be wondering why none of them considered defecting to his party in the first place.

The problem seems to be that the popular appetite for centrism in politics exists largely in the imagination of politicians. Insofar as it exists, judging by the models of Mr Blair and Mr Cameron, as well as the gradual dissolving of the LibDem vote, it’s as a desire for one of the two main parties to tack to the centre, rather than an urge to find some new centrist party.

Scotland is, of course, in a different position because of the SNP which – leaving aside its different sort of independence – governs in the slightly left-of-centre social democratic tradition to which the new group appears to be aligned, and with much the same attitude towards Brexit.

As it happens, none of the new group’s MPs represents a Scottish seat. But it would be interesting to know what kind of market there is for a Unionist, anti-Brexit but essentially Blairite kind of party. Instinctively, one imagines that there would be quite a lot of support for such a group. The reality, however, seems to be different when the electorate gets into the polling booth. Amazingly, almost 40 years after its foundation, the SDP still officially exists, separately from the Liberal Democrats. But you’d hardly know it. I rather doubt that the Independent Group will manage even that level of survival.

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