Purpose: Half of British university students experience assault and harassment behaviours; few report them. Bystander intervention training has been recommended as a means of reducing these behaviours, but there is little evidence about their potential effectiveness in UK contexts. The purpose of this paper is to understand UK students' attitudes towards reporting and intervening in sexual assault, harassment and hate crimes. Design/methodology/approach: A mixed methods cross-sectional survey (n=201; 75.6 per cent women) was conducted in one British university. Open text data were analysed using thematic analysis. Findings: Students considered harassment and assault unacceptable, and were confident to intervene in and likely to report incidents. However, fear of backlash was a barrier to intervening and reporting, and they felt that victims should decide whether to report incidents. Students perceived perpetrators as being ignorant about what constitutes consent, harassment and assault. They identified a need for university community education about this and how to report incidents and support peers. Research limitations/implications: This cross-sectional survey was conducted at one UK University. The data might not reflect other students' attitudes, and may be subject to response bias. University community bystander training should be acceptable, report and support systems might be utilised by students. This may have potential to reduce prevalence and increase reporting. Practical implications: University community bystander training should be acceptable, report and support systems might be utilised by students. This may have potential to reduce prevalence and increase reporting. Originality/value: This is the first study to investigate UK student attitudes to prosocial bystander behaviours.