In London, place a hundred on account (5)
I believe the answer is:
acton
'in london' is the definition.
(area of London)
'a hundred on account' is the wordplay.
'a hundred' becomes 'ton' (I've seen this before).
'on' means one lot of letters go next to another.
'account' becomes 'ac' (abbreviation for account).
'ton' after 'ac' is 'ACTON'.
'place' acts as a link.
(Other definitions for acton that I've seen before include "London area" , "somewhere in London" , "District of West London" , "Part of the London borough of Ealing - British historian, d. 1902" , "Gladstone's adviser" .)