Poem by a Northern diner, drunk on beer (11)
I believe the answer is:
draughtsman
'poem' is the definition.
(thesaurus)
'a northern diner drunk on beer' is the wordplay.
'a northern' says the letters should be written backwards (in a down clue, letters go up or 'north').
'diner drunk' becomes 'nams' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' means one lot of letters go next to another.
'beer' becomes 'draught' (draught beer is a type of beer).
'nams' in reverse letter order is 'sman'.
'sman' after 'draught' is 'DRAUGHTSMAN'.
'by' is the link.
Can you help me to learn more?
(Other definitions for draughtsman that I've seen before include "One makes plans" , "jumps over others on board" , "Person qualified to produce scale drawings" , "potential king" , "One making plans" .)