Most Britons play as members of the orchestra (11)
I believe the answer is:
trombonists
'members of the orchestra' is the definition.
The definition and answer can be both people as well as being plural nouns.
Perhaps you can see an association between them that I can't see?
'most britons play' is the wordplay.
'play' indicates an anagram.
'most'+'britons'='mostbritons'
'mostbritons' with letters rearranged gives 'TROMBONISTS'.
'as' is the link.
Can you help me to learn more?
(Another definition for trombonists that I've seen is " some brass".)