Branching out, police officer introduces poetic technique (15)
I believe the answer is:
diversification
'branching out' is the definition.
'police officer introduces poetic technique' is the wordplay.
'police officer' becomes 'di' (detective inspector).
'introduces' means one lot of letters go next to another (some letters come before or introduce others).
'poetic technique' becomes 'versification' (writing verse).
'di'+'versification'='DIVERSIFICATION'
(Other definitions for diversification that I've seen before include "Making more variety" , "Process of widening one's range of activities" .)