Centrist leader, second-class, left impression (5)

I believe the answer is:

blair

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'centrist' is the definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?

'leader second-class left impression' is the wordplay.
'leader' becomes 'l' (this could be a standard abbreviation of which I'm unaware).
'second class' becomes 'b'.
'left' is a reversal indicator.
'impression' becomes 'air' (I've seen this before).
'l'+'b'='lb'
'lb' in reverse letter order is 'bl'.
'bl'+'air'='BLAIR'

Can you help me to learn more?

(Other definitions for blair that I've seen before include "5,27 [PRIME MINISTER]" , "A political leader" , "George Orwell's real name" , "former leader" , "Former prime minister" .)

I've seen this clue in The Sun.

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