Photo: Andrew Matthews/PA Archive/PA Images

If late-night chatter in the bars of SW1 about realignment could be converted into votes, centrist politicians would be well on their way to governing Britain. Labour defections? A new party? Vince Cable’s plans for a less tribal politics, with his successor possibly drawn from outside parliament? All are possible; but can any of them break through at Westminster?

Here is the good news for centrists. The democratic world has humbled big incumbent parties in recent years in ways that seldom happened in the half century after the Second World War. Until the new century, the broad pattern in most countries was for centre-right and centre-left parties to dominate the democratic landscape. Today, some have crashed, others shrunk and, in two cases been taken over by total outsiders. If party competition has become so much more fluid, then surely Britain’s political centre, facing one party obsessed by Brexit and another lead by a self-proclaimed Marxist, should be on a roll?

Now for the bad news. Outsiders have broken through in three particular circumstances. None offer succour to Britain’s centrists.

1. A proportional, or semi-proportional, voting system. Nationalist parties from Sweden andGermany to Greece and Italy all established an initial bridgehead in the country’s parliament with well under 20 per cent of the vote. In the UK, first-past-the-post punishes such parties, unless they have geographically concentrated support (such as the SNP). Ukip, the Greens and the Liberal Democrats have all found this to their cost. So, of course, did the short-lived Social Democratic Party in the 1980s. In economists’ terms, first-past-the-post presents a very high barrier to entry. This is great for stability, but terrible for challenging useless incumbents.

2. A two-ballot presidential system where the big traditional parties have fallen out of favour. Emmanuel Macron was especially fortunate. Although he defeated Marine Le Pen massively in the run-off, by 66-34 per cent, he won only 24 per cent in the first round. True, he held a narrow lead; but the four leading candidates all won 20-24 per cent. Given the dynamics of a personality- rather than party-driven election system, and a two-ballot system in which many voters see their first-round vote as a chance to let off steam rather than choose a government, there is a fair chance that Macron would have fallen at the first hurdle in a…

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