Hello Tim & Robert, I wasn't intentionally keeping you guys in the dark with the fix, I'd updated the thread title and put an update message at the top of the original post, then was tied up with something else before I could get back to the PC to add this entry.
Thanks to assistance from Mike, we found that the UV filter was still in place in the lamp assembly. This step had been missed prior to the unit being shipped. It's a relief to know it was something fundamental, but the experience has been worth while as I've learnt considerably more about the B9C and its operation whilst troubleshooting.
Thank you to everyone that took time to comment and add their advice and thoughts, apologies again that you had a wait a while for the outcome, it was not my intention.