Like some coppers and throw open cash till (5,7)
I believe the answer is:
plain clothes
'like some coppers' is the definition.
The definition suggests a plural noun which matches the answer.
'throw open cash till' is the wordplay.
'throw' is an anagram indicator.
'open'+'cash'+'till'='opencashtill'
'opencashtill' with letters rearranged gives 'PLAIN-CLOTHES'.
'and' is the link.
Can you help me to learn more?
(Other definitions for plain clothes that I've seen before include "Mufti" , "sort of detective" , "Ordinary attire" , "Policeman's non-uniform wear" , "uniform? Wrong" .)