Grew ponytail to supply admission of error (7,7)
I believe the answer is:
written apology
'admission of error' is the definition.
'grew ponytail to supply' is the wordplay.
'supply' indicates an anagram (in a supple way).
'grew'+'ponytail'+'to'='grewponytailto'
'grewponytailto' with letters rearranged gives 'WRITTEN APOLOGY'.
I've seen this clue in The Everyman puzzle in The Observer.
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