Quantitative data on physical activity and health behaviours during the UK COVID-19 lockdown. The anonymous web-based survey was performed between 6th April and 22 April 2020, approximately mapping to weeks 3-5 of the lockdown in the UK.  The main survey included 49 questions which covered a broad range of topics including (1) Demographics, (2) Health and Health Behaviours, (3) Adherence to COVID-19 Control measures, (4) Information sources used to learn about COVID-19, (5) Trust in various information sources, government and government decision-making, (6) Rumours and misinformation, (7) Contact & Communication during COVID-19 and (8) Fear and Isolation. This data set includes 20 variables and 9,190 responses. It relates to medRxiv submission MEDRXIV/2020/098921 - Version 1.