I get around 30-37 mpg out of mine average. I once got 40.1mpg
but it can go down to around 25mpg if it gets a booting! 
I doubt very much that you get 30-37 average out of a VR.
Unless you drive around like a granny!
I've got a 16v and i usually average 31-35 over a lot of miles, mixture of town/single carriageway/motorway, highest i've seen is 43 think on a long run.
I usually get 300-330 out of a tank so 250-300's not bad for a VR6.
Tank on mine is 50 litres so presumably it's the same on a VR.