Perhaps jumbo's assuming animal sanctuary is somewhere near Mayfair? (4,4)
I believe the answer is:
park lane
'somewhere near mayfair?' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'perhaps jumbo's assuming animal sanctuary' is the wordplay.
'perhaps jumbo' becomes 'plane' (I can't explain this - if you can you should believe this answer much more).
'assuming' is an insertion indicator (inserted letters are taken in or assumed).
'animal sanctuary' becomes 'ark' (as in Noah's Ark).
'plane' placed around 'ark' is 'PARK LANE'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for park lane that I've seen before include "road outside Dorchester hotel" , "Expensive Monopoly property" , "London street - with 22d" .)