Asturias56. Of course I can't tell you in advance whether my drive will be delayed any more than I can tell you whether my flight will be delayed, nor can I tell you next weeks lottery winning numbers.
Logic dictates you leave in plenty of time, then adjust your speed and route of progress accordingly, not so hard to do with modern technology.
What you do highlight with that comment is the added flexibility of driving over flying, if there is adverse weather for instance I can just set off earlier or even the day before, you can't necessarily do that when you have a flight booking you are committed to.
My journey times to LGW have been between 5 and 10 hours, LHR 4 hours and 7 hours....hence the reason I say LGW was more beneficial to me than LHR.