You dont say what model or engine you have (100,110,120, 130??) this could well make a difference to your consumption figures.
Mines a 120.
Also it raises the question about return from different diesel outlets(Tesco's,Esso ,Shell comparisons)
Perhaps this warrants raising as a new thread ' selwonk ' if you're reading this!!
I believe the same inquiry was carried out about 5 years ago using a diesel golf as the testing tool .
The guy filled up at different garages over a period of time and logged returns in mpg from the different suppliers of diesel.
As I recall there was quite a considerable difference over main supplier (ie Shell bp esso as to supermarket brands and it was summed up as additives being in the main manufacter brands that made the diesel burn cleaner ,hence more miles for your money!)
What about starting a new poll to establish diesel returns from different fill up
outlets and we report in and see who gets the best return on who evers diesel