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Way
of
viewing
a
group
regularly
infiltrated
by
police
constable
(6)
Way of viewing a group regularly infiltrated by police constable (6)
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The definition is at the beginning of the clue.
How the clue works
Way of viewing is the definition. Take "a set" (a group) and insert PC (police constable) into it — but "regularly" tells us to split the set around the PC, giving A-S-PC-ET, which spells ASPECT.