Easy
You get on the ferry at Portsmouth, Plymouth, Newhaven or Dover.
Get off in France
Drive on the wrong side of the road for about 1250 miles passing through Spain on the way and you're there.
Alternatively if you have good sea legs, a strong constitution and fancy less driving, get the ferry to Bilbao or Santander.
Sounds straightforward enough. Tell me more about driving on the wrong side of the road, is that the same as driving on the correct side of the road with the steering wheel on the wrong side of the car.