This research note explores the mechanisms behind age differences and changes over time in one of the two major value dimensions in British politics, libertarian-authoritarianism. I show that the British electorate has become substantially more libertarian over the last 30 years, but that older people have remained more authoritarian than younger people over this period. Conventionally, due to the problem of the under-identification of models containing age, period and cohort variables, it is difficult to assess whether this indicates generational differences, and generational change, or not. This paper overcomes some of these problems however, by measuring social ageing factors, such as marriage, and using panel data to rigorously assess how individuals change due to these social ageing factors. I find little evidence of psychologists’ claims that social ageing leads to increases in authoritarianism, and conclude that both age differences and changes over time are generational in nature.