‘It was a joint plan we worked out together’. How the I-WOTCH programme enabled people with chronic non-malignant pain to taper their opioids: a process evaluation by Martin Underwood, Kate Seers, Charles Abraham, Harbinder Kaur Sandhu, Vivien P Nichols, Sam Eldabe, Alleyne Sharisse, Balasubramanian Shyam, Betteley Lauren, Booth Katie, Carnes Dawn, D Furlan Andrea, Haywood Kirstie, Iglesias Urrutia C Paola, Lall Ranjit, Manca Andrea, Mistry Dipesh, Noyes Jennifer, Rahman Anisur, Shaw Jane, KY Tang Nicole, Taylor Stephanie, Tysall Colin, Underwood Martin, J Withers Emma