Period in which British will exhibit sound tone (6)
I believe the answer is:
timbre
'tone' is the definition.
(I know that tone can be written as timbre)
'period in which british' is the wordplay.
'period' becomes 'time period' (period of time).
'in which' indicates putting letters inside.
'british' becomes 'br' (abbreviation for British).
'time' enclosing 'br' is 'TIMBRE'.
'will exhibit sound' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for timbre that I've seen before include "The distinctive property of a voice" , "Character (of sound)" , "Distinctive tone" , "Characteristic quality of sound" , "Quality of sound of the voice" .)