In the middle of town, diners cursed the proprietors (6)
I believe the answer is:
owners
'the proprietors' is the definition.
('owner' can be a synonym of 'proprietor')
'in the middle of town' is the wordplay.
'in the' becomes 'own' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'middle of' indicates the central letters.
'town' becomes 'aldershot' (I've seen this before).
The middle of 'aldershot' is 'ers'.
'own'+'ers'='OWNERS'
'diners cursed' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for owners that I've seen before include "Holders, possessors" , "Those in lawful possession, as of house" , "Worsen for possessors" , "Legal possessors" , "Proprietors" .)