Will the rising share of ethnic minorities in western societies spark a backlash or lead to greater acceptance of diversity? This paper examines this question through the prism of the UK Independence Party (UKIP), the most successful populist right party in British history. The paper contributes to work on contextual effects by arguing that ethnic levels and changes cross-pressure white opinion and voting. It argues that high levels of established ethnic minorities reduce opposition to immigration and support for UKIP among White Britons. Conversely, more rapid ethnic changes increase opposition to immigration and support for UKIP. Longitudinal data demonstrates that these effects are not produced by self-selection. The data further illustrate that with time, diversity levels increase their threat-reducing power while the threatening effects of ethnic change fade. Results suggest that the contextual effects literature needs to routinely unpack levels from changes. This also suggests that if the pace of immigration slows, immigration attitudes should soften and populist right voting decline.