Originally Posted by
GentleGiant
Thanks.
Any hints as to how you tracked it down so fast? Keen to learn

Sure.
There's only one BA209 on 22nd, so pretty sure it's G-BNLL. So, to back it up:
3 flights to Miami on 22nd December, one BA209 - G-BNLL.
Easy when you know how
I just wish there were similar sites for non-ba aircraft.