This article uses the World Anti-Slavery Convention of 1840, and the way in which it was represented in Benjamin Robert Haydon's painting of it, to reflect on the ways in which Britons thought of themselves as an ’imperial people’, ’lords of humankind’, fit to rule over others. The Whig reforms of the 1830s had brought the enfranchisement of large numbers of middle-class men, and the emancipation of the enslaved across the British Empire. Excavating the assumptions of the abolitionists who gathered at the Convention allows us to see how new hierarchies of difference were encoded by 1840, placing freed black men, middle-class women and Irish Catholics on the margins of the new body politic.