Hi, the drive down is easy, you can do it with one sleep about halfway, near the Pyrenees and stay in 'Quick Palace Anglet' where you pay by card at the machine by the door
But 1 sleep is very 'matchsticks'.... 2 or 3 stops is infinitely better.
If you have a good tdi estate car, it is cheapest to fill up in Northern France nit Southern UK , one tank will get you to the Pyrenees and the second tank down to HO
Tunnel is cheapest and ferry crossings get rough this time of year
Longer crossings are best if it's ferry if you can sleep across the Channel
If you set out from the Midlands or further North you really need a sleep across the channel or in Northern France.
Crossing to Santander on Pont Aven is the best.... Sleep and cruise all the way across Biscay and very easy drive through Spain
Ferries are very booked up though now, which makes it impossible to plan around the rough/windy crossings because you have to book well in advance