Hi lenny,
Glad to see another U.K. Vx owner. I have had my VX now for 7 months. Over this period of time I have compiled parts numbers for the more general consumables i.e. air filters oil filters etc. I'm afraid you will not get great fuel consumption from the VX and as it runs better on Shell Optimax it will cost you slightly more. I guess you have checked that the air filter is in good condition, I get about 325 miles from a £65 fuel up not great but then the vehicle is such fun to drive. If you get any problems with the windows or the reversing camera/hifi screen let me know as I have gone through all this. You will find this site a great source of info and Scotts's Moncha site gives you loads of tech. info.
I am in the process of looking into some uprated brake pads from EBC and trying to find the part numbers for the wheel bearings. I get my parts from St Charles Isuzu in the states.
Again welcome to VX ownership in the U.K.
There are a few of us U.K. owners who use this site.