This thesis investigates British attitudes towards immigration, a key issue in the 2016 EU referendum. As its primary contribution to the literature, it demonstrates that British people can become more positive about immigration after exposure to a short text. The thesis draws on literature relating to political psychology, notably as regards authoritarianism and the Dual Process Model. It touches on behavioural science, the study of individual differences (including Moral Foundations Theory, Social Dominance Theory and personality traits) and the literature on framing. In the initial pre-registered survey experiment, over 11,000 British people were exposed to short pro-immigration texts reflecting different theoretical approaches in an “intervention tournament.” The experiment showed that attitudes towards EU immigration could become more positive but failed to identify the most effective approach. A study was then carried out (total N>30,000) to investigate the underlying drivers of immigration attitudes, establishing that authoritarianism is one of the best predictors of anti-immigration attitudes in the UK. An additional literature review then considers the literature on authoritarianism, including research by Adorno et al. (1950), Allport (1954), Altemeyer (1981), and Feldman & Stenner (1997). It also discusses Social Dominance Theory (Pratto et al., 1994) in the context of the Dual Process Model (Duckitt, Sibley, 2009). The next pre-registered experiment tests how these characteristics fit together. It establishes that a sub-dimension identified as Authoritarian Aggression is of particular interest. In the final pre-registered experiment (N>9,000), texts framed to reflect authoritarian values are tested. Those exposed to an authoritarianism compatible text were significantly more positive about immigration than those exposed to a control. The thesis includes a published paper which shows how this research and its associated methodologies can be relevant in other fields and outside of the UK. A framing experiment about attitudes towards climate change was carried out in seven countries (N>14,000) in collaboration with the Foreign, Commonwealth and Development Office and the Economic and Social Research Council (ESRC).