Major airfields have a double letter at the end of their designator.
EGLL - Heathrow
EGKK - Gatwick
EGCC - Manchester
EGFF - Cardiff
and so on.
That's about the only thing I've noticed. There are geographical groupings, but they're loosely based. Newcastle - NT, Humberside - NJ and NV that I can never remember. But then Leeds is NM and if my geography serves me correctly and it does tend to get hazy north of Watford it's West from that lot