[Question] Are mice or rats (as pests) a potential area of animal welfare improvement?

Several of my friends have had mice or rats in their houses. Pest.co.uk claims (with a bizarre amount of accuracy) that there are 19,846,504 rats in London. I would guess that London has relatively few rats per person compared to other cities with less frequent garbage/​waste disposal.

In my friends’ experience, humane traps don’t work very well and so some of them regretfully use snap-style traps.

How many rats are there in cities, and could this be a potential area to improve animal welfare? E.g. through banning cruel traps, or designing better humane ones. I’d be interested to learn if there are any organisations working on this.