Imitating policeman leads to your insisting 'Not guilty!' (7)

I believe the answer is:

copying

'imitating' is the definition.
('copy' can be a synonym of 'imitate')

'policeman leads to your insisting not guilty' is the wordplay.
'policeman' becomes 'cop' (I've seen this before**).
'leads to' suggests taking the first letters.
The initial letters of 'your insisting not guilty' is 'ying'.
'cop'+'ying'='COPYING'

(Another definition for copying that I've seen is " Transcribing".)

I've seen this clue in The Telegraph.

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