Discovers sectarians being troubled (10)

I believe the answer is:

ascertains

'discovers' is the definition.
(ascertaining is a kind of discovering)

'sectarians being troubled' is the wordplay.
'being troubled' is an anagram indicator.
'sectarians' anagrammed gives 'ASCERTAINS'.

(Other definitions for ascertains that I've seen before include "Discovers" , "Finds out" .)

I've seen this clue in The Times.

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