British remain in port (5)
I believe the answer is:
brest
'port' is the definition.
(I know that Brest is a port)
'british remain' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'remain' becomes 'rest' (synonyms).
'b'+'rest'='BREST'
'in' acts as a link.
(Other definitions for brest that I've seen before include "French port" , "Naval base in Brittany" , "French warships here in Brittany" , "French Atlantic naval base" , "Port in Brittany" .)