Down under, the Briton may not take my part (5)
I believe the answer is:
pommy
'down under' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?
'the briton may not take my part' is the wordplay.
'the briton' becomes 'pom' (pom is a kind of briton).
'may not' becomes 'y' (I can't justify this - if you can you should give a lot more credence to this answer).
'take' indicates putting letters inside.
'part' indicates taking the first letters.
The first letter of 'my' is 'm'.
'pom'+'y'='pomy'
'pomy' enclosing 'm' is 'POMMY'.
Can you help me to learn more?
(Other definitions for pommy that I've seen before include "British person (Australian colloquial)" , "Abusive term for English" , "Victorian Englishman" .)