This paper presents a case study of the emergence of the issue-linkage necessary for a cross-cutting EU cleavage to become electorally salient. We argue that a key political decision on immigration in 2004 facilitated the emergence of a new dimension of party competition and growth in popular support for the United Kingdom Independence Party (UKIP) leading eventually to the 2016 EU Referendum. To examine this thesis we trace the impact of the UK's government's immigration policy on (i) rising immigration, (ii) the political salience of immigration, (iii) the increasing association between concern about immigration and Euroscepticism, and (iv) the emergence of a cross-cutting dimension of party competition coalescing around support for UKIP. The analysis combines information from official immigration rates, media reporting on immigration, Mori polls, Continuous Monitoring Surveys, and the British Election Study.