The real lesson of the 1820s, however – not dissimilar to the realisation which has dawned on American isolationists in different times – was that the doctrine of non-intervention, while seductive and logical, ultimately proved to be finite and unsustainable.

In October 1827, in the battle of Navarino in Greece, Britain joined forces with the French and Russians to sink the joint fleets of the Ottoman Sultan and the Pacha of Egypt. The episode was the decisive moment in the Greek campaign for independence from Ottoman rule.

However, the British government had not wanted to intervene militarily on behalf of the Greeks, and certainly not for the sake of humanitarian reasons or the Philhellenism which had drawn Byron and other volunteers to the struggle. In reality, the British fleet had been sent to the region, and a deal struck with Moscow and Paris, to prevent the Russians intervening independently and gaining a stranglehold in the region. The battle of Navarino itself was an accident, sparked when the Turkish and Egyptian fleets had unexpectedly fired on the British and French, provoking the following. Members of the government were furious and believed a dangerous precedent had been set. The following year, the King’s Speech did not refer to it as a glorious victory in the name of freedom, but an ‘unfortunate event’.

Canning had died two months before the battle took place, though he had been instrumental in preventing unilateral action by Russia. In the years before his death, however, he had become increasingly aware of the limitations of British non-intervention. As he put it in 1823, ‘the course we had to pursue was on a path which lay across a roaring stream; attempts might be made to bear us down on the one side or the other’.