Anything said to come from Portsmouth (5)
I believe the answer is:
aught
'anything' is the definition.
('aught' means anything)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for aught that I've seen before include "Anything at all (archaic)" , "Emphatically anything" , "Nothing" , "Anything (Shakespearean)" .)