Power of special constable to intercept drug smuggler (6)
'power' is the definition.
(I've seen this before)
'special constable to intercept drug smuggler' is the wordplay.
'special constable' becomes 'SC' (abbreviation for special constable).
'to intercept' is an insertion indicator.
'drug smuggler' becomes 'mule' (I've seen this in other clues).
'sc' inserted within 'mule' is 'MUSCLE'.
'of' is the link.
(Other definitions for muscle that I've seen before include "Might, perhaps", "for bearing around?", "Strength - to move limbs, etc", "Brawn", "Body tissue that effects movement".)