AJP Taylor, How Wars End
Later there was a congress about giving a blessing to Austria for intervening in Naples. And then there came something they hadn't expected -- there was a liberal movement in Spain. And with this liberal movement there were the beginnings of a civil war. [Tsar] Alexander at once claimed that here was the great opportunity for the Holy Alliance. There should be a strong military intervention against liberal leaders in Spain, and the strong intervention should be provided by the Russian army. This did not meet with British approval at all. Not for the first time and certainly not for the last, the British government took the view that if there was to be a liberal government out of hand somewhere, it should be allowed to lead its country to destruction, but there should not be an intervention by the great powers against this movement.
[The Duke of Wellington, at the next congress, voiced Britian's veto of a Holy Alliance intervention in Spain.]
As a matter of fact, a very simple way of dealing with the Spanish liberals was then discovered. It was found that Great Britain had no objection if a neighbouring state intervened. The French at that time being very conservative and also somewhat anxious to use their army which had been out of work ever since 1815, intervened in Spain and restored the absolute monarchy. The British made no complaint[...]