Allotment site behind health centre (10)
I believe the answer is:
Here is my best explanation:
'allotment' is the definition.
('allocation' can be a synonym of 'allotment')
'site behind health centre' is the subsidiary indication.
'site' becomes 'location' (**).
'behind' is a charade indicator (letters next to each other).
'centre' indicates the central letters.
The central letters of 'health' are 'al'.
'location' after 'al' is 'allocation'.
(Other definitions for allocation that I've seen before include "Distribution, assignment" and "Apportionment".)