British command having the edge (6)
I believe the answer is:
border
'the edge' is the definition.
(synonyms)
'british command' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'command' becomes 'order' (order is a kind of command).
'b'+'order'='BORDER'
'having' is the link.
(Other definitions for border that I've seen before include "Line that indicates a boundry" , "Frontier of a country" , "Edge or boundary" , "Type of sheepdog" , "Boundary line" .)