Background In May 2016, the UK announced standardising packaging legislation for tobacco products. There was a 12-month transition period with both branded and standardised packs on the market until May 2017. The aim of this study was to investigate whether the implementation of standardised packaging in England was associated with changes in illicit tobacco and cross-border purchasing.

Methods We used Smoking Toolkit Study data covering the time period from 2012 to 2020. We ran time-series analysis using Autoregressive Integrated Moving Average with Exogenous Variable models to investigate the monthly changes in illicit tobacco and cross-border purchasing in England. The model was adjusted for other tobacco control policies implemented during the relevant time period and tobacco pricing. We used May 2017 as an implementation point and run sensitivity analysis using July 2016 and February 2017 as alternative implementation points given phased introduction of the policy.

Results The average prevalence of illicit tobacco and cross-border purchasing in the past 6 months was 14.4%. The implementation of standardised tobacco packaging legislation was associated with a monthly decline in illicit tobacco and cross-border purchases after May 2017 by 0.16% per month (beta=−0.158, 95% CI −0.270 to −0.046). The results were robust to considering different implementation points for the policy (July 2016: beta=−0.109, 95% CI –0.213 to −0.005; February 2017: beta=−0.141, 95% CI −0.245 to −0.036).

Conclusions In contrast to the tobacco industry’s argument that the legislation would lead to an increase in the illicit tobacco and cross-border market, this study demonstrates that the implementation of the policy is associated with a decline in illicit tobacco and cross-border purchases in England.