Imbecile Cockney journalist wearing black coat (6,6)

I believe the answer is:

donkey jacket

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'coat' is the definition.
(donkey jacket is a kind of coat)

'imbecile cockney journalist wearing black' is the wordplay.
'imbecile' becomes 'donkey' (I can't justify this - if you can you should give a lot more credence to this answer).
'cockney journalist' becomes 'ack' ('hack' - I've seen this before - said with the 'H' dropped - a cockney accent.).
'wearing' is an insertion indicator.
'black' becomes 'jet' (similar in meaning).
'ack' put into 'jet' is 'jacket'.
'donkey'+'jacket'='DONKEY-JACKET'

Can you help me to learn more?

(Another definition for donkey jacket that I've seen is " Garment associated with building workers".)

I've seen this clue in The Times.

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