Methods
We used an inductive, semistructured interview design, informed by topic guides to ensure that the discussion remained relevant to addressing the study aims, while allowing flexibility for participants to raise issues they perceived as salient. The study involved concurrent data collection and analysis, which allowed issues identified in early interviews to inform questions asked in later ones. Research ethics (Cambridge Central Research Ethics Committee: 18/EE/0084) and governance approvals were obtained in conjunction with approvals for the wider trial.