In a courtly way, he's like a London Baron (4)
I believe the answer is:
This clue could be a double definition.
'in a courtly way he's like a london' is the first definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'baron' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for earl that I've seen before include "Countess his wife" , "Male member of British nobility" , "Rank immediately above viscount" , "British nobleman" , "Essex, say" .)