Dalo,
Actually all I did in the end (and was amazed it worked OK

) was go into my C: drive, highlight the WoW folder and opt to move it to the D: drive.
After initially getting a message to say it would take 21 hours

it eventually only took a couple of minutes and all my WoW files now appear in the D: partition and there is now 7.9 extra gigs of space in the C: drive.
I have not actually tried to play WoW yet on there so I hope the blinking thing recognises I have moved it.
Thanks for all your help. No doubt I'll be back.
Dave