Mice are attracted to confined spaces and food. In some parts of London, the buildings are residential areas above shops and restaurants, offering mice the perfect combination of an abundance of food to eat and places to hide. When the shop below is closed at night, mice can move through the walls to the restaurant below, avoiding the tenants in the residence above. In the morning, when the tenants wake, the mice return to the residence above to escape the tenants working in the restaurant. Canals tend to restrict the movement of mice, though they can swim. Shops and residences near canals are more likely to have mice infestations because of this. Even when mice are removed from a house near a canal, they may use the canal or the banks of the canal as an escape route to move to a new, safe area. The tube system in London is low-traffic as far as people are concerned, allowing mice to use the tunnels as an underground highway system so long as they avoid the trains. With so many places to hide and countless ways to get there, architecture has made eradicating mice in London next to impossible.
While the architecture of London does contribute to the mice's ability to thrive in London, it does not explain how they became so prevalent in the first place. There are many places in London that do not have any of these architectural or environmental qualities, meaning architecture can't account for the mouse infestation in these areas.