Couples in British competitions (6)
I believe the answer is:
braces
'couples' is the definition.
('brace' can be a synonym of 'couple')
'british competitions' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'competitions' becomes 'races' (race is a kind of competition).
'b'+'races'='BRACES'
'in' acts as a link.
(Other definitions for braces that I've seen before include "Supports for men's trousers" , "Over-the-shoulders supporters" , "They hold up men's trousers" , "Support for trousers" , "Couples" .)