Eek that is a nasty shock to find for sure. I am no fan of rats, but a couple of years ago we had a nest at the bottom of the garden. I actually saw the babies all running onto the bird table and sliding down the pole in the middle again and again. They looked so cute and were having fun just as all young creatures do.
We stopped feeding the birds for a while, kept an eye out that they didn't come close to the house, and after a few weeks they moved on of their own accord :-)While all this rat activity playground was going on our Dog would just lie further up the garden sunbathing and watching!!