Flag of British queen and king (6)
I believe the answer is:
banner
'flag' is the definition.
(I know that banner is a type of flag)
'british queen and king' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'queen' becomes 'anne' (Queen Anne, 18th-century queen).
'and' means one lot of letters go next to another.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'b'+'anne'+'r'='BANNER'
'of' is the link.
(Other definitions for banner that I've seen before include "Web page header; flag" , "Knight's standard" , "Streamer, flag" , "Ensign" , "Flag bearing a device" .)