Individual with a small part, Starmer’s not one to break law (no shock) (6-2)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

“Keir”(Starmer, UK PM) minus ( not ) “I”(Roman numeral for “one”) contained in ( to break ) [ LAW + anagram of ( … shock ) NO ]. Defn: …, namely, a walk-on role in a play or other forms of entertainment.