A particular incident on GWR this time last year springs to mind, wherein a Paddington -> Carmarthen service made an unscheduled stop at Swindon for a relief driver to board, and this somehow resulted in over half a dozen passengers getting stranded after they were allowed off the train for whatever reason... I would suspect TOCs would rather not run the risk of something like this happening again and having to suffer the resulting bad publicity.
www.railforums.co.uk
Passengers stranded after being let off train for fresh air
Couldn't find this if already posted. BBC News Train passengers were left "distressed" and "confused" when the driver of a packed train encouraged them to get off at a station for some fresh air – only to leave without them. Trevor Greenfield, 74, and his wife, Eileen, 68, were among the group...