In response to the COVID-19 pandemic, the UK Government placed society on 'lockdown', altering the gambling landscape. This study sought to capture the immediate lockdown-enforced changes in gambling behaviour. UK adults (n = 1028) were recruited online. Gambling behaviour (frequency and weekly expenditure, perceived increase/decrease) was measured using a survey-specific questionnaire. Analyses compared gambling behaviour as a function of pre-lockdown gambling status, measured by the Brief Problem Gambling Scale. In the whole sample, gambling participation decreased between pre- and during-lockdown. Both gambling frequency and weekly expenditure decreased during the first month of lockdown overall, but, the most engaged gamblers did not show a change in gambling behaviour, despite the decrease in opportunity and availability. Individuals whose financial circumstances were negatively affected by lockdown were more likely to perceive an increase in gambling than those whose financial circumstances were not negatively affected. Findings reflect short-term behaviour change; it will be crucial to examine, at future release of lockdown, if behaviour returns to pre-lockdown patterns, or whether new behavioural patterns persist.