Prune helped when going (3,3)

I believe the answer is:

saw off

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'prune' is the definition.
(I've seen this in another clue)

'helped when going' is the wordplay.
'helped when' becomes 'saw' (I am not sure about this - if you are sure you should believe this answer much more).
'going' becomes 'off' (I've seen this in another clue).
'saw'+'off'='SAW OFF'

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(Other definitions for saw off that I've seen before include "Forced to leave" , "escorted to departure" , "lop" .)

I've seen this clue in The Independent.

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