Background: The Covid-19 pandemic had a profound effect on the delivery of healthcare research. Covid-19 research was prioritised and many non-essential trials were paused. This study explores the engagement experiences of trial participants', PPIE contributors' and trial staff during the Covid-19 pandemic and towards recovery and restoring a diverse and balanced UK clinical trials portfolio., Methods: Interviews and focus groups were undertaken with PPIE contributors, trial participants and trial staff members from NIHR research trials across the UK (November 2020-June 2021) across portfolio specialities: Cancer, Oral and Dental Health, Musculoskeletal Disorders, Cardiovascular Disease, Neurological Disorders, Primary Care, and Conditions associated with susceptibility to Covid-19 (Diabetes, Stroke, Respiratory Disorders). Topic guides were developed for each participant group and interviews were conducted over Zoom. The transcripts were analysed using codebook thematic analysis in NVivo (V.12)., Results: 106 participants comprising, 45 PPIE contributors, 27 trial participants and 34 trial staff members were recruited. Three themes to engagement with trials during Covid-19 were developed. 1) Ensuring continued contact. Continued and tailored communication, having a trial point of contact and regular updates all enhanced trial engagement and retention. Patients' unfamiliarity with materials being sent electronically reduced engagement and trust. 2) A balanced move to remote consultations. Remote follow-up and monitoring were convenient and allowed for wider recruitment across the UK. Participants were more likely to discuss personal subjects in their own homes. Remote visits lacked a personal touch, some concerns over missed diagnoses or being unable to appreciate the situation, technical abilities or equipment failures were seen as barriers, especially for disadvantaged or older people. 3) The importance of feeling fully informed. Factors that supported attendance were knowledge about trial conduct adherence to Covid-19 regulations, social distancing, clear signage at the site and opportunities to ask questions. Barriers included not knowing what to expect and not feeling safe with rules and regulations., Conclusions: Our findings highlight a number of ways to future proof trial delivery against future pandemics or disruptions such as offering online options to participate in research, ensuring consistent communication between participants and the research team, making sure participants feel fully informed and the continued reassurance of safety in the clinical setting., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Leggett et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)