This article examines how English radicals reacted to the challenge of Irish nationalism in the mid nineteenth century. The Young Ireland, Fenian and Home Rule movements brought forth responses from across the spectrum of English radicalism, but scholars have neglected this topic, even as they have emphasized the importance of continental nationalisms for understanding English radicalism. This article, drawing on the radical press and manuscript sources, argues that a belief in the exceptional nature of the United Kingdom constitution, together with the growing importance of the imperial interest, convinced English radicals to reject Irish nationalism.