Is there a scientific element in the current crisis of the British Labour Party? A touch of chaos theory perhaps? Or something genomic – what biologists call an “antagonistic gene” – which causes the party every 30 years or so to fall into the political equivalent of a civil war?

You could argue that there always has been and always will be a struggle for mastery between the hard Left and a social democratic wing that lurks even in the quieter times, ready to erupt with venom when tensions reach a critical point, usually after electoral defeat.

Clem Attlee (who led the most successful Labour Government ever between 1945 and 1951) caught this rather well in an interview towards the end of his life in the mid-1960s. Asked about “rebels in the party”, he replied: “We have had experience of them all the time. You have always got certain quite genuine left-wingers and you have always got a number of queer birds. Sometimes you can use them, like Aneurin Bevan, and sometimes you can’t.”