There's some confusion here regarding "Bio Diesel".
People are using the term "Bio Diesel" for 2 different fuels.
1) The more common usage if for using used chip shop oil.
Some people process this at home, others just bung it straight in. Some mix it 50:50 with pump diesel.
If you collect waste chip oil you area s likely as not to get a waste carriers license from your local council.
Another process is to methylate the veggie oil - this makes it for all intents and purposes the same as dino diesel.
2) The second fuel called "Bio Diesel" is what the oil refineries use and blend in with dino diesel.
This is labelled B7 which means it may contain up to 7% of FAMEs - fatty acid methyl esters produced by methylating virgin veggie oil.
Be aware - there is B10 around and B20 is coming round the corner.
For this the refineries use veggie oil harvested from the fields - maize, corn oil. The oil can be converted to ethanol - see the previous posts ^^^ or methylated.
Either way you are taking away food stock
These bio diesel fuels are good BUT they have low sulphur content and that's bad for engine lubricity. So they add an additive package at the refinery to the diesel.
You can buy your own additives which also improve the cetane rating - as discussed above ^^^
There is no ethanol in bio diesel and diesel users will not experience the troubles the older petrol vehicles have.
Using premium pump diesel is not really needed - but in running the odd tank through you will notice the extra oomph due to the increase in cetane rating. Again, you have to balance the cost of premium fuel against the extra mpg gained.
Please note: It's not a good idea to run the CAV DPA fuel pumps on waste or virgin veggie oil
Even if you blend it with pump diesel. The CAV pumps can't take it and will soon seize up, they are metered for a different viscosity of fuel
The Bosch injector pumps love the stuff !
Of course there's always the one exception to the rule, who will claim they've been running on waste oil for years with no problems