Objectives: To analyse enrolment to interventional trials during the first wave of the coronavirus 2019 (COVID-19) pandemic in England and describe the barriers to successful recruitment in the circumstance of a further wave or future pandemics. Design: We analysed registered interventional COVID-19 trial data and concurrently did a prospective observational study of hospitalised patients with COVID-19 who were being assessed for eligibility to one of the RECOVERY, C19-ACS or SIMPLE trials. Setting: Interventional COVID-19 trial data were analysed from the clinicaltrials.gov and ISRCTN databases on July 12, 2020. The patient cohort was taken from 5 centres in a respiratory NIHR network. Population and modelling data were taken from published reports from the UK government and MRC biostatistics unit. Participants: 2,082 consecutive admitted patients with laboratory-confirmed SARS-CoV-2 infection from March 27, 2020 were included. Main outcome measures: Proportions enrolled, and reasons for exclusion from the aforementioned trials. Comparisons of trial recruitment targets with estimated feasible recruitment numbers. Results: Analysis of trial registration data for COVID-19 treatment studies enrolling in England showed that by July 12, 2020, 29,142 participants were needed. In the observational study, 430 (20.7%) proceeded to randomisation. 82 (3.9%) declined participation, 699 (33.6%) were excluded on clinical grounds, 363 (17.4%) were medically fit for discharge, and 153 (7.3%) were receiving palliative care. With 111,037 people hospitalised with COVID-19 in England by July 12, 2020, we determine that 22,985 people were potentially suitable for trial enrolment. We estimate a UK hospitalisation rate of 2.38%, and that another 1.25 million infections would be required to meet recruitment targets of ongoing trials. Conclusions: Feasible recruitment rates, study design, and proliferation of trials can limit the number, and size, that ill successfully complete recruitment. We consider that fewer, more appropriately designed trials, prioritising cooperation between centres would maximise productivity in a further wave. / Dr Burge and Prof Stewart declare funding from a Cancer Research UK Major Centre award (C9685/A25117). Dr Coyle declares funding from the British Heart Foundation. Dr Gkrania-Klotsas is supported by an NIHR Greenshoots personal Award from the Clinical Research Network. Prof Kanagaratnam declares funding from the Imperial College COVID-19 Research Fund. Dr Knolle declares funding from MRC CARP. Dr Torok declares support from a Clinician Scientist Fellowship (Academy of Medical and the Health Foundation) and the NIHR Cambridge Biomedical Research Centre. Dr Warne receives funding from the National Institute for Health Research Cambridge Biomedical Research Centre at the Cambridge University Hospitals NHS Foundation Trust. Dr Yates’ salary is funded by The British Society for Rheumatology and Versus Arthritis. Dr Matheson declares funding from MRC (CSF MR/P008801/1) and NHSBT (WPA15-02). Dr Li declares funding from the Medical Research Council programme MRC_MC_UU_00002/10. Dr Villar declares funding from the Medical Research Council (grant number: MC_UU_00002/15). Dr Toshner is funded by the NIHR Cambridge Biomedical Research Centre. This work was enabled by co-operation of the NIHR Respiratory Translational Research Collaboration.