Thanks for your responses Anurag / Brian
@BrianJ I had actually read and attempted to reverse engineer this methodology to fit my scenario prior to my initial posting. Had another bash after reading your response. Unfortunately without success in both cases 
. I might be misinterpreting how to apply it for the solution I need - would have been elegant if I had been able to.
I’m now of the opinion that I might be over complicating things somewhat and should try another approach.
Grateful to the both of your assistance
Kind Regards - Grant