As I said, I can get better than 1000km from a tank for country driving, which is basically all I do. Average consumption, calculated not from the OBC, is 8.6 litres/100km. When my wife drives the X for extended periods, the consumption gets closer to 8.0 litres/100km.

There are lots of variables at play, however, even for purely country driving. The standard 235/65R17s reduce the fuel use due to less rotational inertia and less aero drag compared to bigger wheel/wider tyre combinations; driving with the windows or the sunroof open degrades the aero efficiency; roof racks/bars etc also degrade the aero efficiency; the driving environment, ie, hilly or flat is also critical; how much load you have in the vehicle is also critical. And, of course, things like tyre pressures, the mechanical condition of the vehicle, the condition of your air filter, etc, all play their part, as does your driving style.

Our's is a 3.0d Sports with 19s but with no sun roof. So I don't know whether the rolling resistance will be contributing to the consumption we're experiencing.

Anyway, I have now switched off the auxilary heater, so it will be interesting to see what kind of consumption OBC will be recording.