Mice in London are quite a common occurrence above all in older houses and modern tower buildings. The main reason is down to how we build our buildings and also how we alter them over time.
Mice are common in London to start with. They can easily be seen in the London tube network, and running along old building in central London. From there it is only a matter of getting in and getting out. Most of the pest control London call outs that Inoculand attends reveal that mice can simply squeeze in through a damaged air vent, or a gap below a door.
Once the mice gain access within London houses or buildings, they have no trouble traveling within the walls or underneath the floorboards. In itself that would not necessarily be a major issue if it was not for the way most builders, plumbers and electricians run pipes and cables. As the pipes go through the walls or floors, they are not sealed around. When we check the space under the kitchen for the presence of mice droppings, we normally find huge gaps at the base of the walls and often we see the day light through the hole the builder created to fit the PVC sink drain.
The cost to remediate to such issue is not only down to the pest control price, but can only be answered with a shift in behaviour and culture from both trade contractors and clients. Too often cutting corners in order to keep cost low and profit high.
Simply put, the issue is not the method of construction as such, but rather the level of care that the operative applies to the job. The most heart breaking example I came across was a top end penthouse on the river that was done to a beautiful finish. They were plagued with mice because in first place the management failed to control the mice at building level, second because the electrician had not bothered plugging the holes he made through the plasterboards when he runs his wires.
So here you have it. Mice in London are quite common in houses principally because of the low standard of handiwork at building stage and mismanagement of the pest control mice infestations from neighbours possibly down to the pest control cost associated to it.