I am also very **** about my fuel economy. You have to be when it costs so much over here. I have fuel records for all my cars from 1984 and I have done over 350,000 miles in the past 20 years (MS-Excel can be a wonderful tool).

When I boot the XF, I get between 290 and 310 miles per tank. I was driving economically as an experiment to see how far I could get on my last tank, and I was extremely surprised to get 426 miles. I have calibrated my speedo, tripometer, and odometer and they are basically accurate.

I have the Upsolute Chip and we are near to sea level in the UK. I did not need the air-con much during my experiment.

Anyway, I am going to repeat it in September using 98RON fuel to see if there is a difference.

It is much more fun to boot it!!!! It seems that hard acceleration is where the fuel gets burned the quickest.