Resigns and has Charles deputise for (6,2,2)

I believe the answer is:

chucks it in

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'deputise for' is the definition.
I know nothing about this answer so I can't tell whether this works.

'resigns and has charles' is the wordplay.
'resigns' becomes 'siti' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' becomes 'n' (common abbreviation for 'and').
'has' means one lot of letters go next to another.
'charles' becomes 'chuck'.
'siti'+'n'='sitin'
'sitin' put after 'chuck' is 'CHUCKS IT IN'.

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I've seen this clue in the Evening Standard.

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