Thanks for the replies and opinions. I would never expect the driver to get involved in "forcing" a passenger off. But I do think the bus shouldn't move until the space is clear. If this was a general policy then buggy users would know there's no point in refusing to move. It does feel like discrimination to board a couple of other pax at the stop and then drive off leaving my mother.On this occasion there was plenty of space on the bus, just the buggies didn't want to move.
I've noticed the SL5s are quite busy on Saturdays, what with having a single deck only. I can envisage a situation where the buggies can't move (even when folded) because of lack of space. That did happen once in the past = the kind mother insisted on getting off the bus to allow my mother on, even though we were happy to wait. And of course we've had the situation where a chair is already onboard when we want to get on. I feel sorry for couples in wheelchairs. They can never travel together on buses. I suppose it's quite rare.