Brian: where on earth do you get the idea that going from Dunkerque is seventy miles further than Calais? The two ferryports are only 24 miles apart by road, see map below! Even if Vic were to drive from Dunkerque West to Calais before he started off for Spain it would add less than 24 miles. However, Google Maps shows the direct distance from Calais to Bilbao as 1,204km and from Dunkerque West as 1,210km so the actual additional distance to Spain would appear to be about 4 miles. I am sure that one of our truck drivers can confirm this or point out where it is wrong.
Vic: one of my colleagues has just driven to Spain a couple of months ago and it sounds like a marathon work-up to me. Not helped by the fact that he took a wrong turning on the way down, despite his Tom Tom, and went off on a giant detour! He lives at the Dover end of Temple Ewell so is presumably round the corner from you, perhaps I could put you in touch?
Portsmouth - Le Havre does not sound as if it offers much of a saving as you have to drive to Portsmouth in the first place.