It may be carried on though by-laws forbid it (6)
I believe the answer is:
litter
'it may be carried on though by-laws forbid it' is the definition.
The definition suggests a singular noun which matches the answer.
'it' is the wordplay.
I cannot really see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is located in the answer.
The remaining letters 'liter' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for litter that I've seen before include "waste material" , "Odds and ends of rubbish left lying about" , "little ones?" , "Sow's young" , "Rubbish strewn about the streets" .)