Favourite here in the middle - safe (5)
I believe the answer is:
peter
'safe' is the definition.
(slang term for a safe)
'favourite here in the middle' is the wordplay.
'favourite' becomes 'pet' (synonyms).
'in the middle' says to take the centre.
The centre of 'here' is 'er'.
'pet'+'er'='PETER'
(Other definitions for peter that I've seen before include "Safe - name for a man" , "prison cell" , "Fellow < safe" , "Saint's name" , "Leading apostle" .)