Jolly good police officer, some say (5)
I believe the answer is:
super
'jolly good' is the definition.
(I've seen this before)
'police officer some say' is the wordplay.
'police officer' becomes 'supe' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'some' says to take the centre.
'say' becomes 'express' (to express something is to say it).
The middle of 'express' is 'r'.
'supe'+'r'='SUPER'
Can you help me to learn more?
(Other definitions for super that I've seen before include "senior cop" , "Informally great, really up there" , "Gushily great, excellent" , "Incomparable" , "Informally terrific, splendid" .)