Ignore rag about church worker in singalong (9,5)

I believe the answer is:

gregorian chant

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'singalong' is the definition.
I can't judge whether this defines the answer.

'ignore rag about church worker' is the wordplay.
'about' indicates an anagram.
'church' becomes 'ch' (common abbreviation).
'worker' becomes 'ant' (worker is a type of ant).
'ignore'+'rag'='ignorerag'
'ignorerag' with letters rearranged gives 'gregorian'.
'gregorian'+'ch'+'ant'='GREGORIAN CHANT'

'in' acts as a link.

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(Other definitions for gregorian chant that I've seen before include "variety of plainsong" , "Medieval plainsong" .)

I've seen this clue in The Daily Express.

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