Strange to be focused mainly on City of London? (9)
I believe the answer is:
eccentric
'strange' is the definition.
(synonyms)
'on city of london?' is the wordplay.
'on' says to put letters next to each other.
'city' becomes 'EC' (postcode for the City of London).
'of london?' becomes 'centric' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ec' put next to 'centric' is 'ECCENTRIC'.
'to be focused mainly' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for eccentric that I've seen before include "Unconventional type" , "Odd one" , "Odd or unconventional" , "Unconventional, a bit strange" , "Unconventional or unusual" .)