The use of behavioural science interventions, and particularly social norms, in tax compliance has become a growth industry for scholars and practitioners alike in recent years. However, these interventions largely represent a ‘black box’, where effects could be explained by a pro-social desire to support one’s community, conditional cooperation, desire to conform, or fear of reprisals. We conduct an experiment in local government taxation in the United Kingdom which tests social norms against a control condition and against messages that highlight the enforcement process. Social norms outperforms enforcement salience, suggesting that this explanation, although more powerful than the control, does not fully explain compliance effects. By comparing results to previous studies, we find that these effects are larger for local taxes than national ones, even when comparing similar taxpayers. This provides further evidence that social norm type interventions can be most effective when using norms from socially closer reference groups.