Had turned and left (4,3)

I believe the answer is:

gone off

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'left' is the definition.
(thesaurus)

'had turned' is the wordplay.
'had' becomes 'gone' (I can't justify this - if you can you should give a lot more credence to this answer).
'turned' becomes 'off' (synonyms).
'gone'+'off'='GONE OFF'

'and' acts as a link.

Can you help me to learn more?

(Other definitions for gone off that I've seen before include "exploded" , "Having turned bad" .)

I've seen this clue in the Evening Standard.

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