I think you must have been away a long time! Halfway round the M25 isn't in my "pleasant" book.
M1 to M4 is not much more than a stone's throw!
I'm sure the reason NWI-AMS has survived all these years is 90% to do with the Southern North Sea gas industry, not the difficulty of road connections to Heathrow.
You worked for Air UK and/or KLM UK did you?