I feel I have to defend the 220D here. I have a '56 Plate, which when new struggled to return over 36mpg even on motorway journeys. As per all the other comments 6th was useless unless it was doing 80mph+
The fuel economy has slowly but surely improved as the mileage has increased - Usually returning around 40mpg for a motorway trip, cruising at 80mph once it passed about 15K
The car has now just passed 30K, and I have noticed a huge difference in the way it drives and performs in relation to mpg. Cruising at 80mph it's now returning 45mpg per tank, and for the last few weeks I have tried cruising at 70-75mpl in 6th which now feels perfectly acceptable, and the car is returning 50mpg per tank. Couldn't be happier!
I think it's a case of the more miles the better with this one.
oh, and for reference this is on standard derv from Tesco.