It was my Mercedes-AMG ForFour Black Series Brabus Edition 1 of 1
The ML 63 - with either engine - would manage 19.x MPG on that trip, and GT C might manage 23 MPG. My wife thought I was nuts going so far in the ForFour but at the end of the journey I was as fresh as a daisy despite having been sat in it for more than 6 hours in total.
I really enjoyed it and it was comfortable too. I had one scary moment joining the motorway from the services - a short slip with a hard stop at the end, and fast lorries - meant that I was moments away from getting stuck on the slip, but other that the only other thing lacking was the audio quality, which could be improved easily.
The most efficient car I’ve ever had was a 1997 Rover 220 SDi which did 46 MPG no matter how hard - or soft - I drove it. Many years later I had a 2014 Audi A6 3.0 Bi TDi [313] Quattro Sport Line Black Edition (and it really was called that, blooming ridiculous!) and I managed 46 MPG once, but I had to work hard for it! Maybe it was the weight of all the badges