We drove approx 1540 miles at an average speed of 53mph and a consumption level of 47.8mpg. The fuel consumption was just over 50mpg on the way down, but French diesel seems to be a lower quality fuel, delivering higher consumption and rough-running from the engine.
After our first fill-up and subsequent long journey to Strasbourg I was actually worried that something might have gone wrong with the car, as the engine was clearly vibrating more than it should. After the second refueling it ran much better for the journey home, although still a little rough. I've since almost completely drained and refilled with fresh Tesco diesel, and added injector cleaner. It seems smoother and hopefully will be fine.