A 54 plate Focus should be OK on biodiesel from the pump - using recovered
waste oil is a slightly different story and generally requires some minor
mods to your engine.

Biodiesel wont harm your engine; in fact it will do it a power of good!  You
may find that as you start using higher concentrations regularly that the
fuel filters will need changing a few times within a thousand miles or so,
but don't worry as this is only a temporary thing ;)

Wish I could have a found a diesel focus when I changed my car recently, but
there just weren't any in a decent condition in my area and I was a bit
pushed for time...