I'm hoping that when I get back, linux will be able to sort the disk out but I suspect I'll probably end up having to take it back.
Well, no luck with (g)parted, looks like the drive is actually broken. The size is reported correctly, but the entire space is unallocated. It refuses to let me create a new file system, from the looks of it, the drive reports itself as being write protected, despite having no write protect switch.
Brilliant. It'll be the weekend before I have a chance to return it to the shop I bought it from.