Did some reading up on it all first, and found that the BMWs engine will run on B100 (100%) BioDeisel
Gave the chap a call, and arranged for him to open his garage for me after I finished work and he sold me £40's worth @ 75p/litre - nearly 30p/litre cheaper than the petrol station selling regular derv.
It conforms to the European standard, and needs no diesel mix to stop it freezing, though he did recommend mixing 20% regular when it gets really cold.
My BMW also runs a fuel cooler in the engine bay - Im going to cover this for the winter so the fuel doesnt get to cold and thick.
Although its cheaper, I have noticed a slight performance loss, but nothing that 75p/litre doesnt fix - especially when my 100mile commute just involves cruising on the motorway
The 75p/litre covers all tax and Duty on the fuel, and you get a recipt to prove you have paid your taxes should you get stopped