Reduced numbers affect town's referral centres (5)
I believe the answer is:
fewer
'reduced numbers' is the definition.
'affect town's referral centres' is the wordplay.
'affect town' becomes 'few' (I can't explain this - if you can you should believe this answer much more).
'centres' indicates the central letters.
The middle letters of 'referral' are 'er'.
'few'+'er'='FEWER'
(Other definitions for fewer that I've seen before include "Reduced" , "smaller number of people" , "in smaller numbers" , "Less in number" , "Not so many" .)