
Not UK advice but that from CERF in USA given at the bottom:
http://www.vmdb.org/dec98.html"Entropion is a painful and potentially blinding disease and therefore affected dogs in breeds that have a high incidence of entropion (such as Bloodhounds, Chow Chows, English Bulldog, Bull Mastiff, Chinese Shar Pei, Mastiff, Vizsla, and Saint Bernards) are denied certification. (CERF NOTE: As of November 2001, entropion is breeder's option for Bloodhound, Bulldog, Bull Mastiff, Mastiff, Saint Bernards.) However, because exaggerated facial conformation with loose skin and/or heavy facial folds often leads to eyelids that roll in or out predisposed the animal to irritation, discomfort and possible vision loss, selecting away from these traits in all breeds is strongly encouraged. "
So I would say a resounding no to breeding from an affected animal, a sibling or parent is another matter, assuming the affected was a one off in the litter, if considering siblings, and that the parents had not produced it before/since.