Tough old deputy (8)

I believe the answer is:

exacting

'tough' is the definition.
(I've seen this before)

'old deputy' is the wordplay.
'old' becomes 'ex'.
'deputy' becomes 'acting' (I've seen this before).
'ex'+'acting'='EXACTING'

(Other definitions for exacting that I've seen before include "Not easily satisfied" , "Demanding in effort - or money" , "Difficult and onerous" , "Insisting upon" , "Arduous and demanding" .)

I've seen this clue in The Independent and The Telegraph.

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