Title holder from circle in London borough (7)
I believe the answer is:
baronet
'title holder from circle in london borough' is the definition.
'baronet' can be an answer for 'title' (I've seen this before). I'm unsure of the 'holder from circle in london borough' bit.
'title holder from circle in london borough' is the wordplay.
'title' becomes 'baron' (aristocratic title).
'holder from circle in london borough' becomes 'et' (I can't justify this - if you can you should give a lot more credence to this answer).
'baron'+'et'='BARONET'
Can you help me to learn more?
(Other definitions for baronet that I've seen before include "Lower noble" , "Hereditary knight" , "Tone bar (anag.)" , "Aristocrat" , "A Bronte (anag.)" .)