The official position can give rise to a duty to act, and failure to act can then become the actus reus of a crime.
This is unlike in some countries whose law requires every person to act in situations where another is in danger or distress
R v DYTHAM (1979)
Dytham (a police officer) witnessed a violent attack on the victim but took no steps to intervene or summon help; instead he drove away from the scene. The officer was guilty of wilfully and without reasonable excuse neglecting to perform his duty