Issue of voting system abandoned by British (5)
I believe the answer is:
allot
'issue' is the definition.
(thesaurus)
'voting system abandoned by british' is the wordplay.
'voting system' becomes 'ballot' (I've seen this before).
'abandoned by' is a deletion indicator.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'ballot' with 'b' taken out is 'ALLOT'.
'of' acts as a link.
(Other definitions for allot that I've seen before include "Dispense or distribute" , "Dedicate" , "budget" , "Dish out" , "Apportion (something to someone)" .)