Oh London offices do have mice problems. I work at Canary Wharf and last year sat on a trading floor infested with mice.

The mice would come out in the evenings. You'd know because first you'd hear one of the salespeople scream. Then the more macho traders would rush around banging on desks, trying to flush out the by now petrified mouse...

The trading floors also had small cafes ('trader delis'). One day I found a dead mouse on the counter next to the cafe's credit card machine. I took a photo as I knew noone back on the trading floor would believe me.

At that point, the cafe was closed for the day and thoroughly cleaned. The cleaners also started removing all food from people's desks.

The best solution imo would have been cats...

In London on average you are never more than 10ft from a rat, or so they say. For everyone 100ft from the nearest rat there is someone 1ft away from 10 rats.

Paris has also a rather big rat problem, even if they are usually hidding in the sewers/subways, but one can easily see them at dusk going through the trash. Also we had a few rats in our (19 century) flat, according to a person living above us.