Last spring and summer I tried running with veg oil in my older disco (300 Tdi) by mixing rape seed oil (34p a litre) into the tank with normal diesel. I reckon I got up to about 75% veg oil to 25% mineral diesel with no problems. Moved back to 100% diesel for winter and changed the filters to avoid problems with waxing.
The info about fuel having 5% bio fuel from January is useful, I may need to modify my mix.
I don't recommend this for cold weather as the veg oil goes like jelly when cold, but it worked well and even seemed to make the engine run smoother.
Not sure whether I'm brave enough to run the TD5 on this yet.
Don't forget to inform the revenue if you do this, you're allowed 2500 litres without paying duty so keep all your receipts as proof, and don't forget that customs related records need to be produced for up to 7 years after the event.