I just, finally, after living here for two years, managed to navigate the parking permit website well enough to be able to buy a clutch of parking permits for visitors (we don't have a car ourselves because we're smug - or is it the other way round?).
And as usual with (local) government websites, once you've done it, you can't remember why it felt so difficult in the first place. It did require me to upload a current utility or council tax bill, maybe it was that? Or maybe I made a mistake before with my credit card details? Or maybe there wasn't an 'r' in the month last time I tried. Dunno.
All I know is that now my mother-in-law can park outside my house all day without fearing the arrival of a traffic warden. And there aren't any silly scratch cards or stickers to put in/on the car, I just need to remember her registration number.
Although next year we're going through local government reorganisation, so no doubt there'll be a whole new system to grapple with.