Prodigal son first to talk about breaking regressive law (7)
I believe the answer is:
wastrel
'prodigal son' is the definition.
(thesaurus)
'first to talk about breaking regressive law' is the wordplay.
I cannot quite see how this works, but
'first' could be 'a' and 'a' is present in the answer.
'about' could be 're' (regarding) and 're' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for wastrel that I've seen before include "Worthless person" , "Useless person" , "Prodigal" , "Layabout" , "Spendthrift" .)