Medieval England was proudly Catholic and ostentatiously loyal to Rome. But from the late sixteenth century until recent times – and even now – anti-Catholic prejudice has been a cornerstone of English and British identity. This lecture will look at how this prejudice grew out of the persecution of Protestants in the 1550s, at the idealistic historian who crystallised it, and at the political crises, real and invented, which turned his text into a paranoiacs’ charter.