I like to take the train, but living a little way north of London (on the East Coast main line) does make things a bit variable. It would be the same, I suspect, in any direction from the capital, since orbital trains are rare. Only doing events up to 200km (and therefore not starting before 8am) does help.
Cambridge and Huntingdon events are easier by train than by car from here. South of Cambridge (Henham/Ugley) means going via Cambridge, or towards London and then out again, either of which adds so considerably to time that I've sometimes compared how long it would take to ECE them, but chickened out. I've done most of the ACME Witham events by train, but it takes twice as long as by car, which is mostly an issue for getting home again early enough to have an evening with my wife. Dunmow no longer has a station, so is Henham plus a ride.
Chalfont is not that far but just hopeless from here in train terms. Reading is difficult, and I usually steal what is notionally my wife's car, although I did manage the Robert Boyle one by train because it started in the town centre, whereas most of the others I've done have been a bit south or north.
Stevenage doesn't even qualify as an ECE of course, and needs neither train nor car