Lots of response:- molto grazie. In an attempt to respond to allI have tried a vast array of boots, in fact one of my misfit Scarpas is the SL mega wide jobbo. I haven't looked at Patagonia, so thanks for that. I don't use crampons: being a devout coward, and happy with a summer ML ticket, I avoid snow, ice or the prospect thereof unless it's fine powdery stuff.
I think the problem here is a latent one which I can't explain but seems to fit the facts. Ten years ago I was knocked off a motorcycle and broke both bones in my left shin, and spent eleven months in plaster. Since then the arch of my foot has been higher on one side than the other, but until about two years ago I didn't have any trouble with walking boots, running shoes or cycling shoes. I assume as I develop my geriatric tendencies, my feet, along with all my other faculties, are beginning to fail. Dismal prospect, really.
Anyway, thanks for all your help, and if I find a solution I'll post a thread for it.