Complete in diplomacy (6)

I believe the answer is:

intact

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

'in diplomacy' is the wordplay.
'diplomacy' becomes 'tact' (I've seen this before).
'in'+'tact'='INTACT'

(Other definitions for intact that I've seen before include "Undiminished" , "Entire and complete" , "Inviolate" , "Not damaged or missing a part" , "Unscathed" .)

I've seen this clue in the Evening Standard.

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