Key fact in reproduction method where crosses accumulate (7,7)
I believe the answer is:
polling station
'where crosses accumulate' is the definition.
(you mark a ballot paper with a cross)
'key fact in reproduction method' is the wordplay.
I cannot quite understand how this works, but
'key' could be 'g' (musical key) and 'g' is found within the answer.
'fact' could be 'stat' (statistic) and 'stat' is found within the answer.
'in' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for polling station that I've seen before include "Choosing place" , "essential part of reproduction" , "School temporarily perhaps" , "It gets my vote!" .)