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I've just been looking again. It seems, as CaC suggested, that in order to scan via wi-fi you have to use 'software' that came with the printer.
As I'm using a notebook now (no disc aperture) I assume it's not possible.
It was very much a 'one-off' so I'm not to bothered. I was hoping someone had a simple, obvious to everyone but me, fix.
Anyway, thanks for all your help again.