Deny wife escaping old prison (6)
I believe the answer is:
negate
'deny' is the definition.
(negate can mean to deny or refute)
'wife escaping old prison' is the wordplay.
'wife' becomes 'w' (abbreviation).
'escaping' suggests deleting specific letters.
'old prison' becomes 'newgate' (former London prison).
'newgate' with 'w' removed is 'NEGATE'.
(Other definitions for negate that I've seen before include "Contradict" , "Cancel; invalidate" , "Show to be false" , "Render ineffective" , "Cause to have no effect" .)