In order to become a ‘registered supporter’ of the Labour party, you first have to disclose whether you’re a member of an organisation opposed to the Labour party. Such as, I suppose, the Labour party. You also have to affirm that you agree with the party’s ‘aims and values’, which must be the hardest bit, because who alive now knows what those are?

If the leader of the Labour party — to pick an example not wholly at random — agrees with the aims of the Labour party, then how come he just voted against the party’s own manifesto in order...