Hi John - looked in my programmes and found an Epson Twain V.5 driver, which I uninstalled as you suggested. It then accepted a fresh download from the Epson site (the latest being the Windows 7 version). I then clicked on the scanner in Control Panel - Devices, only to get the same message as before - "WIA driver required for this device".
So its looking very much like my options are: a) say goodbye to the scanner, or b) fork out to Vuescan for their driver (which worked in the free trial - complete with the Viewscan watermark!).
As I only use the scanner occasionally, I don't think I'll be giving Viewscan my cash anytime soon. Its a shame, because it scans photographs exceptionally well!