Objectives The UK’s withdrawal from the European Union (a political movement known as ‘Brexit’) incited concern both in the public and private sector about the future of drug development and the clinical trial landscape in the UK. This study evaluates trends in the initiation of phase III clinical trials that evaluated systemic anticancer treatments from 2010 to 2022 both in the UK and worldwide.

Methods and analysis Relevant clinical trials were identified through ClinicalTrials.gov. Initiation date in each country was defined as the date that a study’s record was updated to include a recruiting site in the country of interest. Concurrent clinical site counts were defined as the number of facilities that contemporaneously hosted trials. Temporal trends in trial initiation and site counts were evaluated.

Results Our analysis uncovered a worldwide increase in clinical trial initiation from 2013 to 2019. The UK experienced a decrease in clinical trial initiation immediately post-Brexit in 2020 but rebounded in 2021. The UK’s resurgence in clinical trials in 2021 was driven predominately by industry-funded trials. Other countries saw a similar increase in clinical trial initiation from 2020 to 2021.

Conclusions The UK’s trends in phase III oncology clinical trial initiation from 2010 to 2022 largely reflects global trends, suggesting that other factors (eg, COVID-19 pandemic) beyond Brexit, may have had a stronger influence on clinical trial initiation within the UK.