Plundered mains supply -- there's still hope (3,11)
I believe the answer is:
nil desperandum
'there's still hope' is the definition.
(Latin phrase meaning do not despair)
'plundered mains supply' is the wordplay.
'supply' indicates an anagram (in a supple way).
'plundered'+'mains'='plunderedmains'
'plunderedmains' with letters rearranged gives 'NIL DESPERANDUM'.
(Other definitions for nil desperandum that I've seen before include "Never give up" , "Soldier on" , "Don't despair" , "don't give up hope" .)