Flat landlord no longer observed legal requirements (4,6)
I believe the answer is:
dead letter
'flat landlord' is the definition.
'dead letter' can be an answer for 'landlord' (I have seen 'Unresponsive landlord' mean 'dead letter' so perhaps 'landlord' could also mean 'dead letter'). I am not certain of the 'flat' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for dead letter that I've seen before include "Unresponsive landlord" , "Itll not lead to prosecution" , "Ineffective rule" , "no longer observed" , "Law no longer enforced" .)