Productivity, population growth (and impact on housing and services), population aging (and impact on social care and NHS), societal and cultural changes and conflicts, national identity, etc are all linked to immigration.

The issue is compounded by the fact that successive governments say they want to be tough on immigration, but actually do the opposite. This is what pushes voters to Reform UK and away from the Tories, among other things. Labour is now doing the same (relatively tough talk but no actual effective action).