Bio 20 is probably 20% bio, 80% petro-diesel, the other stuff at 15p below petro diesel price is probably full biodiesel.
I've used it on & off for a year, but beware - don't go to 100% bio straight away, diesel leaves a varnish on the fuel system that bio strips 7 it can block the fuel filter. Instead go up in increments, but after the first tank of 100% bio change the fuel filter.
I've had very mixed results with bio, from superb through to dog rough running, from diferent garages locally. I even had 32mpg from my wagon when running on good biodiesel, through to 18 mpg from it running on poor stuff.
if I could find a good local reputable dealer who does sales to public (got one locally but no seeling to public at the moment) then I'd use it full time.