Constabulary surrounds flat (7)
I believe the answer is:
tabular
'flat' is the definition.
(I've seen this before)
'constabulary surrounds' is the wordplay.
'surrounds' indicates a hidden word (I've seen 'surrounding' mean this).
'TABULAR' can be found hidden inside 'constabulary'.
(Other definitions for tabular that I've seen before include "(Of data) presented in rows and columns" , "Arranged in rows and columns" , "Flat" , "in an array" .)