Well my pre '92 diesel runs perfectly happily on 100% veggie, as do all XUD's!! Do you mean post '92 Norman??
Aka-it depends on what you call 'bio' diesel: if you drive in Europe that's mainly all you get, a 5% or 10% bio mix, it's almost impossible to find straight diesel in France now, and all diesel engined cars are happy on it, even the new generation of high pressure common rail engines will run on pump bio with no trouble.
When you buy pump bio-diesel at the pumps (try Morrisons) in this country, it's normally a 5% mix at the most, but are you after a proper carbon-neutral bio fuel for an older low pressure mechanical injector engine? If so, you won't find it at the pumps: you'll either have to make it yourself, or use SVO (supermarket veggie oil...don't forget to give Gordon & Tony their tax...) or you can buy it tax-paid over the web from a lot of cottage producers.........do a web search on bio fuel.