Mill about in the shop to an even greater extent (5,4)

I believe the answer is:

still more

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'an even greater extent' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'mill about in the shop' is the wordplay.
'about' indicates an anagram.
'in the' means one lot of letters goes inside another.
'shop' becomes 'store' (synonyms).
'mill' anagrammed gives 'illm'.
'illm' going inside 'store' is 'STILL MORE'.

'to' acts as a link.

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I've seen this clue in the Evening Standard.

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