Curiouser and curiouser. Although I can delete printers from the Printers list, when I Add Printer and it searches for what's around it still comes up with a list of previously installed printers despite them not being switched on. So there is another file somewhere that has the info.
Anyway, this was too painful so I used a GParted Live USB (and a donation) to remove the main partitions from both the SSD, and also the HDD that had remnants of Windows on it (so looked like a dual boot), then did a fresh install which is lightening fast with an SSD.
So problem solved - sort of - but I would really like to know what's going on.
Many thanks for your assistance, Mark.