I'm disgusted about Left's claptrap (4)

I believe the answer is:

blah

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'claptrap' is the definition.
(synonyms)

'i'm disgusted about left's' is the wordplay.
'i'm disgusted' becomes 'bah' (I am not sure about this - if you are sure you should believe this answer much more).
'about' is an insertion indicator.
'left' becomes 'l' (common abbreviation).
'bah' enclosing 'l' is 'BLAH'.

Can you help me to learn more?

(Other definitions for blah that I've seen before include "bunkum!" , "Claptrap" , "Rhubarb" , "Meaningless substitute for tedious words" , "Pretentious waffle" .)

I've seen this clue in The Times.

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