Phenomenal cockney pooch caught in a police trap (10)
I believe the answer is:
astounding
'phenomenal' is the definition.
(thesaurus)
'cockney pooch caught in a police trap' is the wordplay.
'cockney pooch' becomes ''ound' ('hound' - both can mean a dog - said with the 'H' dropped - a cockney accent.).
'caught in' means one lot of letters goes inside another.
'police trap' becomes 'sting' (police operation designed to trap criminals).
'a'+'sting'='asting'
'ound' placed into 'asting' is 'ASTOUNDING'.
(Other definitions for astounding that I've seen before include "Extraordinary" , "Amazing" , "Stunning" .)