I have a 2011 XF-S 3.0d Portfolio - got it in October. Having taken on board advice from other members (especially Peter - thank you!) and swapping to premium diesel with an occasional shot of Millers Oil additive, I now regularly get 32-34mpg locally and an easy 42-46 on long motorway trips. I also do not 'spare the horses'!
If I drop into sport mode I can easily drop that down to low 20's. But that's almost too much fun!
Cheers, Jon