Tithes then will be revised in backstreet (6)
I believe the answer is:
tenths
'tithes' is the definition.
(I've seen this before)
'then will be revised in backstreet' is the wordplay.
I cannot quite see how this works, but
an anagram of 'then' is 'enth' which is present in the answer.
'backstreet' could be 'ts' ('st' backwards) and 'ts' is found in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tenths that I've seen before include "Small portions" , "Tithes" , "Sections" , "tiny portions" .)