Symbol of Conservative and most of opposition? (4)

I believe the answer is:

clef

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'symbol' is the definition.
(I have seen 'Musical symbol ' mean 'clef' so perhaps 'symbol' could also mean 'clef')

I don't understand the rest of the clue.

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(Other definitions for clef that I've seen before include "Treble or bass on a stave" , "Treble or bass symbol?" , "Symbol on stave in musical score" , "Symbol on a stave indicating pitch" , "Staff note" .)

I've seen this clue in The Telegraph.

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