<< Would I be correct in saying that Dan-Air (UK) started this practice back in the 1980s ??? >>
TC . . . you are correct . . and actually it served its purpose well re addressing the potential for callsign confusion where the numerics were the same or very similar . . which occurred remarkably frequently, even in those days.
"Was that for us" ( having missed the company prefix ) "Yep those are the numbers it must be" . . .
whoops ?!
Hearing the last digits as well . . 'CJ' 'MJ' 'MI' 'AY' 'TP' 'MW' 'RW' 'VG' 'YG' or whatever made a difference.
(Maybe) 
Remember the trials and Callsign Confusion Reports we had to submit to OPS . . who then attempted to get the airlines to agree a trip number change to avoid the same potential problems day in and day out on the relevant frequencies (LHR at any rate)
I imagine that it can only be worse today.
Stay safe out there . . 99
