OBJECTIVE: To investigate if daily vigorous physical activity (VPA), adjusted for minutes of moderate physical activity (MPA) performed, differs by socioeconomic position or ethnicity in a large sample of UK children with objectively measured physical activity. DESIGN: Nationally representative prospective cohort study. SETTING: UK children born between 2000 and 2002. PARTICIPANTS: 5172 children aged 7-8 with valid accelerometer data for ≥10 hour on ≥3 days, including 1 weekend day. MAIN OUTCOME MEASURES: Time spent in VPA (>3841 counts per min). EXPLANATORY MEASURES: Maternal education, annual household Organisation for Economic Co-Operation and Development equivalised income, ethnicity. RESULTS: Multivariable linear regression models fitted to explore differences in average daily minutes of VPA (adjusted for MPA, mean accelerometer wear time, season of measurement, age and sex), revealed significantly higher amounts of VPA accumulated as a child's socioeconomic position increased (highest vs lowest level of maternal education: β: 2.96, p: 0.00; annual household equivalised income: β: 0.58, p: 0.00, per £10 000 annual increase). Additionally, children from certain minority ethnicities (Bangladeshi and Pakistani: β: -3.34, p: 0.00; other ethnic groups: β:-2.27, p: 0.02) accrued less daily VPA compared with their white British counterparts. CONCLUSIONS: The socioeconomic and ethnic patterning of vigorous activity observed in this study mirrors parallel inequalities in rates of childhood obesity. Given the stronger association of VPA with adiposity than of MPA, intensity specific differences may be contributing to widening inequalities in obesity. Accordingly, these findings suggest that the current global focus on overall moderate-to-vigorous intensity activity may mask important behavioural inequalities.