Thanks for your input. What I have ended up doing is using the key from I386\pid.inf in my unattend.txt file; the installation now completes succesfully without requesting a key. When I do my deploy windows mini-setup lauches and asks for the COA label product key as I have not entered this in sysprep.inf file. Following this I checked my Windows key using MagicJellyBean keyfinder and the key is the one entered at Mini-setup which is what I would expect. This process meets my requiements although I thought there would have been a more well known way to do it