During the years of Italian unification between 1859 and 1861 Britain was the state outside the Italian peninsula that did the most to undermine and bring to an end the temporal power of the papacy. Indeed, as McIntire has noted, Britain's assistance in the destruction of the Papal States was one of the most important of its contributions to the process of unification. In the light of this it is remarkable to find that only a few years earlier the British reaction to the early years of the papacy of Pius IX was enthusiastic, and that there was a surprising degree of British interest in and governmental support for the pope. For a period of two years between 1846 and 1848 the pope was a central figure who influenced not only the course of Britain's foreign policy but also generated a great deal of interest and support within its domestic politics.

There are a number of ways in which to explain this unexpected entente between Britain and the pope. It is tempting at first glance to assume that British enthusiasm for the pope during these years was due solely to the relief that at last a ‘good’ pope had taken charge in Rome and the hope that his subsequent reforms would transform the government and administration of this stronghold of autocracy. This is true to an extent; there was indeed a genuine welcome in 1846 and 1847 for the concept of a liberal pope.