Following your advice I usually use Shell Diesel (I know you recommend some other varieties), I pass on this advice to others. However I usually get a response along the lines of 'all the diesel comes from the same depot in the same lorries even though it is sold under different names, how can there be a difference?'

Can you please tell me/us at what point the additives that make the fuel better are added? I would like to be able to convince my friends that your advice, that I always take at face value, is indeed valid.