Banned brown sauce in fish where seas freeze (5,4)
I believe the answer is:
south pole
'where seas freeze' is the definition.
(frozen region)
'banned brown sauce in fish' is the wordplay.
'banned' becomes 'out'.
'brown sauce' becomes 'HP' (HP is a condiment brand).
'in' means one lot of letters goes inside another.
'fish' becomes 'sole' (sole is a kind of fish).
'out'+'hp'='outhp'
'outhp' going within 'sole' is 'SOUTH POLE'.
(Other definitions for south pole that I've seen before include "gets very cold!" , "Goal of explorers" , "Antarctic" , "to which Scott came" , "Amundsen got there first, before Scott" .)