The 800th anniversary of Magna Carta came at a time of growing uncertainty about what it means to be British. Contemporary politicians have responded by articulating visions of Britishness, through which they seek to unite citizens behind a common identity. Taking as its focus the myth of Magna Carta, this article examines the rhetoric of Britishness of Gordon Brown and David Cameron. It shows that although both link Magna Carta to the myth of British exceptionalism, Cameron alone defines Britishness against an external ‘Other’. The article also demonstrates that Magna Carta acts as a ‘founding myth’, and that its emergence as such is indicative of a change in Britain's ‘rhetorical culture’.