By 1826, speculating that the next war in Europe would be a ‘war not so much of armies, as of opinions’, Canning suggested that, if involved, Britain ‘will see under her banners, arrayed for the contest all the discontented and restless spirits of the age, all those – who whether justly or unjustly – are dissatisfied with the present state of their countries’. This was humanitarian intervention, but de facto rather than by design.

He was prepared to admit that the prospect frightened him somewhat: ‘The consciousness of such a situation excites all my fears, for it shows that there exists a power to be wielded by Great Britain, more tremendous than was perhaps ever yet brought into action in the history of mankind’. The best prospect, he believed was ‘to content ourselves with letting the professors of violent and exaggerated doctrines on both sides feel that it is not their interest to convert an umpire into their competitor’. But alongside this was the recognition that this ‘equilibrium’ might be impossible to maintain.

Circumspection and hard-headedness were not dispensed with. But here was the crux of the Canningite legacy. It centred not on first principles but on two realisations, made over the course of the 1820s. The first was that non-intervention, while the most attractive option, had severe limitations when diplomacy did not suffice in the face of a direct threat to British interests. The second was that once Britain became drawn into active intervention against less liberal powers, she was always likely to be drawn to the ‘liberal’ or ‘humanitarian’ side.