Ok, I think I was missing something obvious. I had failed to launch sysprep on the PC before capturing the image.
After recapturing the (syspreped) image I have got a bit further. Now when my deploy template finishes the OS deployment phase and begins the sysprep stage it displays the "Setup is configuring your system for first use message", but then gets stuck on the administrator logon page and states that my password is incorrect.
I have checked and double checked that the AdminPass variable is configured correctly as my local administrator account, but it keeps getting stuck on this phase.