I must be the exception.
Now with 117K on the clock I had mine Angel re-mapped, DPF de-cored, EGR blanked and Terra-cleaned (along with cleaning out the throttle body, MAF and the MAP sensor replaced. A small bottle of Rhino had been through the system as well as a can of BG44. I've only ever run it on Shell V-Power Diesel in the 4 months I've owned it.
All this was done within a week of buying the car and both trip meters were reset.
Trip A is used for various observations, for example, last week I did an identical 35 mile motorway run over 3 consecutive days and in similar traffic conditions - one at 70, one at 75 and the last one at 80mph for the duration.
This was in no way scientific, but according to the Computer, @70 it was 52mpg. @80 it was 45mpg but at 75mph it was 55.7mpg!
If I re-set it and do an hours worth of slogging around town it drops to 39-42 (again on the computer)
So I do 70% Motorway (and then it's rarely above 80, mostly under that) and 30% around town, stop start and heavy traffic. According to Trip B, over the 2400 miles I've done in it, I've averaged 45.4mpg.