Milton ignored spurious counterclaims from person laying the blame on him (7)
I believe the answer is:
accuser
'milton ignored spurious counterclaims from person laying the blame on him' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'blame on him' is the wordplay.
'blame' becomes 'accuse ' (I've seen this before).
'on him' becomes 'r' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'accuse'+'r'='ACCUSER'
Can you help me to learn more?
(Other definitions for accuser that I've seen before include "origin of charge?" , "One bringing charges" , "One charging" , "One who brings a charge" , "One to point the finger" .)