To elaborate a bit, "City of London" is not the city of London as one would normally imagine. It is a district only about a square mile large that contains the central business and financial district. It has very little residential zoning and fewer than 10,000 residents (compared to 10 million in greater London). A recent change in law *increased the number of businesses receiving voting power to 32,000, and they nominate a number of voters that scales with their number of employees (and the total far outweighs residential votes).

* Corrected wording to clarify that law change only increases the number of businesses — businesses have had the franchise in City of London for centuries. h/t JumpCrisscross