Firm about the middle (4)

I believe the answer is:

core

'the middle' is the definition.
(core can mean the centre of something)

'firm about' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'about' becomes 're' (regarding).
'co'+'re'='CORE'

(Other definitions for core that I've seen before include "The centre of an object" , "Inner part" , "The innermost part" , "Centre, heart" , "Central zone" .)

I've seen this clue in The Mirror and The Daily Express.

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