Two Labour leaders set to sack head of union for business grouping (8)

I believe the answer is:

keiretsu

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'business grouping' is the definition.
I know nothing about this answer so I can't judge whether this works.

'two labour leaders set to sack head of union' is the wordplay.
'two labour leaders' becomes 'keir' (I can't explain this - if you can you should believe this answer much more).
'to sack' indicates an anagram (sack can mean destroy or spoil).
'head of' indicates taking the first letters.
The initial letter of 'union' is 'u'.
'set' with letters rearranged gives 'ets'.
'keir'+'ets'+'u'='KEIRETSU'

'for' acts as a link.

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I've seen this clue in The Guardian.

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