It is deeply unpredictable. Once you get past Reading West J12, the effects of rush-hour traffic can cause all sorts of hold-ups. Leave yourself hods of time, then you will sail straight through and be twiddling your thumbs at LHR. Cut it tight and there will be An Incident at Slough ....

Edited by veryoldbear on 08/07/2011 at 16:54

if you go a bit early, leave at junction 5 langley, take the A4 towards heathrow, and there are lots of places to park + a mcdonalds about a mile from the airport entrance (t1 and 3) so you can get a coffee and hopefully not pay too much in parking charges at heathrow. if you have a smartphone you can check if the flight has landed and then go in, but terminals 1,1a and 3 are central area, 4 southside, 5 westside, all have different approach roads and it is a long way to drive if you are late. My advice , go early and wait close by outside till about 15 mins after the arrival time, then you will have ample time to get in and park. (thats what i do when I am collecting She who must be obeyed)

Good luck!