but you are burying your head in the sand if you think LHR isn't the primary cause of traffic in and around the M4/M25 interchange.
It isn't, I used to do this drive every day. Most of the traffic on the M4 is going into London and most of the traffic on the M25 is going straight past the airport. If it was all going to/from LHR then the link roads would never be able to cope.