Informs one the cats will follow the girl (9)

I believe the answer is:

announces

'informs' is the definition.
(announcing is a kind of informing)

'one the cats will follow the girl' is the wordplay.
'one the cats' becomes 'ounces' (ounce is a kind of cat).
'will follow' means one lot of letters go next to another.
'the girl' becomes 'ann' (woman's name).
'ounces' put after 'ann' is 'ANNOUNCES'.

(Another definition for announces that I've seen is " Declares".)

I've seen this clue in the Evening Standard.

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