Blood Drinker was a middle-aged man with a monotone Scottish accent, with dark hair and a medium build. His crimes are unknown. Given his nickname, it presumably had something to do with drinking blood.
It was Blood Drinker who entered the chamber where the others were in conversing with Cassandra, and informed them that the SS Silverberg had started shipping water 18 floors up. Cassandra had prophesied this. It was Blood Drinker who called down Mr Knot to help inspect the damage. ("Cassandra" deleted scenes, Series VIII)
Since all the other Canaries except the main characters die in the SS Silverberg, it seems Blood Drinker didn't make it either.
Behind the scenes
Blood Drinker was portrayed by actor Joseph Crilly.
Due to mistakes in editing, Crilly's name still appeared in the credits at the end of the broadcast episode, despite Crilly not actually appearing in the broadcast episode.