Policeman perhaps unfriendly then more pleasant -- though not at first (7)
I believe the answer is:
officer
'policeman perhaps' is the definition.
(I know that police officer is a type of law enforcement officer)
'unfriendly then more pleasant though not at first' is the wordplay.
'unfriendly then' becomes 'off' (I can't explain this - if you can you should give a lot more credence to this answer).
'more pleasant' becomes 'nicer' ('nice' can be similar in meaning to 'pleasant').
'though not at first' means to remove the first letter (the first letter is removed).
'nicer' with its first letter taken off is 'icer'.
'off'+'icer'='OFFICER'
Can you help me to learn more?
(Other definitions for officer that I've seen before include "Person with commission in armed services" , "Responsible type" , "Cop" , "who has a public position" , "Person in position of authority" .)