It’s never been a burden to the poor (6)
I believe the answer is:
surtax
'it's never been a' is the definition.
I can't judge whether this definition defines the answer.
'burden to the poor' is the wordplay.
'burden' becomes 'tax' (I've seen this before).
'to' says to put letters next to each other (I've seen this in other clues).
'the poor' becomes 'sur' (I am not sure about this - if you are sure you should believe this answer much more).
'tax' after 'sur' is 'SURTAX'.
Can you help me to learn more?
(Other definitions for surtax that I've seen before include "extra duty" , "Additional charge" , "Additional levy" .)