In 2012, the UK government announced legislation changes and heightened immigration controls designed to create a 'hostile environment for illegal migration.' We measured changes in psychological distress among people from minoritised ethnic groups compared to White British controls before and throughout the implementation of these policies. We used the UK Household Longitudinal Survey to estimate difference-in-difference models for six ethnic groups (Bangladeshi, African, Caribbean, Indian, Pakistani, and White British) in three eras: pre-policy (2009-2012); (2) transition (2012-2016); and (3) ongoing policy (2016-2020). We calculated the adjusted marginal mean psychological distress score at each era using the 12-item General Health Questionnaire (GHQ). In the pre-policy era, we found higher psychological distress for the Pakistani, Bangladeshi, and Caribbean groups compared to the White British group. We observed patterns consistent with increasing psychological distress during the transition era for the Pakistani and Bangladeshi groups, with further increases in the ongoing era for the Bangladeshi group. Levels of psychological distress the Indian and African groups were similar to the White British group in the pre-policy era and decreased over successive eras. A small decrease was observed in the Caribbean group across policy eras, while levels remained stable in the White British group. We found evidence that psychological distress increased among Pakistani and Bangladeshi individuals following the introduction of hostile environment policies but did not detect increased distress in other ethnic groups. This finding underscores the importance of disaggregating analyses by ethnic group to capture the distinct experiences.