Detectives seen in country garden (8,4)
I believe the answer is:
scotland yard
'detectives' is the definition.
(I've seen this before)
'country garden' is the wordplay.
'country' becomes 'Scotland' (Scotland is a country of the UK).
'garden' becomes 'yard' (I have seen 'American garden' mean 'yard' so perhaps 'garden' could also mean 'yard').
'scotland'+'yard'='SCOTLAND YARD'
'seen in' is the link.
(Other definitions for scotland yard that I've seen before include "Metropolitan Police HQ" , "London force HQ" , "Old London police HQ" , "Detective department of the Metropolitan Police" , "Former police HQ" .)