People tend to behave in a less prosocial way towards individuals who are members of an out-group; there is evidence that this also applies to supporters of political parties (Fowler & Kam, 2007; Iyengar & Westwood, 2015). There are different ways to define an out-group in the political domain: it may consist of voters who identify with a party different to one’s own preferred party or of those who voted for a different party. In the UK, the electoral system results in much strategic voting such that these two groups do not coincide. Using a dictator game implemented shortly after the 2024 UK general election, this paper finds that voters contribute less to out-groups defined in both ways but that the voting behaviour of the out-group is a more significant driver of behaviour. Our results provide evidence on whether preferences or actions of others are important factors in determining how prosocial we are.