BS5839 Pt 1 2017  requires a zone plan to be displayed at the all FA panels including slave panels. My question is, if the building is small with a single zone is there a requirement to display a zone plan? Reading BS5839 it does not state single zone FA systems are omitted from this requirement and I suppose a single zone plan would actually inform the fire service that an alarm actuation covers the whole building, which is useful from a search and rescue perspective.

You've sort of answered your own question! If the zone plan is a decent one with the actual layout rather than just a shaded outline it still has value, otherwise it ticks the BS box with little benefit.