Chief of the Defence Staff Sir Nicholas Houghton is worried that Labour leader Jeremy Corbyn will never use the existing means of defence — Trident — to defend the country. Mr Corbyn is incandescent that a mere Chief of Defence Staff has the sheer effrontery to express a view on a matter that is (apparently) irrelevant to the defence of country but is purely political. One is reminded of the accession of Nero to Rome’s imperial throne in ad 54.

According to the Roman historian Tacitus, it was dirty work by the controlling empress Agrippina that did for her husband Claudius, with the result that Nero, her son from an earlier marriage, was installed as emperor, aged 17. At that time there was trouble on Rome’s eastern frontier. The Parthians (roughly modern Iran) had expelled Radamistus, Rome’s nominee to the throne of Armenia, and were busy plundering the country. This was a clear threat to Rome’s eastern provinces, and (said Tacitus) the Roman people, ‘always eager for topics of conversation’, were deeply concerned: how on earth could a mere 17-year-old deal with the threat? A youth under feminine control was hardly reassuring; and he was still being educated. Private tutors would have little to contribute to battles and sieges and all the other problems of war.

There was, however, another view. Nero could not be worse than Claudius; his tutors were highly experienced men; and Pompey and Augustus had both won battles in their teens. Surely it was command and planning that counted, and that depended on Nero’s advisers; if they were up to scratch, Nero would then appoint the very best man for the job. In the event, the advice was good, and Nero did as he was told: top men took charge, and the Roman show of military might persuaded the Parthians to reach a settlement.

At least the 17-year-old Nero had an advisory council thrust upon him. There would simply be no point in Corbyn having one: it might contain soldiers. Bis peccare in bello non licet, it is said: you can’t make more than one mistake in war. The Labour party has already made it.