Navigator in sanctimonious group (5)
I believe the answer is:
pilot
'navigator' is the definition.
(I've seen this in another clue)
'sanctimonious group' is the wordplay.
'sanctimonious' becomes 'pi' (old-fashioned term for pious).
'group' becomes 'lot'.
'pi'+'lot'='PILOT'
'in' is the link.
(Other definitions for pilot that I've seen before include "who shows the way?" , "Aviator" , "One-off programme" , "Guide, leader" , "experimental programme" .)