David Cameron’s rather clumsy presentation of the case for British membership of the European Union was instantly over-simplified into a warning that a British exit could lead to a Third World War. He left himself open to the mockery of the other side because he overstated his case while failing to explain the subtle ways in which British influence in Europe is an aid to continental stability. His argument reasonably implies that naked rivalry between nation states always has the possibility of turning nasty, particularly when they do not have the habit of routinely negotiating with each other to overcome differences. That requires permanent institutions, which to be effective need as much support as possible, including British support.

Mr Cameron could also have pointed out that a British referendum result in favour of exit could trigger an avalanche of similar demands elsewhere in Europe. What is at risk of unscrambling, therefore, is the fundamental notion of European solidarity. That could lead to an eventual threat of armed conflict of some kind, if not for the present generation then subsequent ones. The EU, sadly, has not abolished original sin.