"No doubt to our US friends, a rat is pretty mundane fare but..."

Good grief, what is that supposed to mean? Arnie, I assure you that we in U.S. do not take rats for granted. We are mostly clean and orderly people, and we don't tolerate rats around our homes.

If you have a rat around your place, go to a store, buy some rat poison, follow the directions, and get rid of it and its fellows.