Hi again Joel,
I did a quick exposure prior to taking the dark so that the shutter was actioned. I then checked the shutter didn't move when I took the dark (took the dark by selecting 'dark' in Artemis), so yes, the shutter was shut (apparently!).
I have informed my supplier and he is going to talk to Atik on my behalf.
Many thanks for your input - I'll post the final outcome.
Regards,
Pete