We had rats one Christmas couple of years ago - our house backs onto a large woodland with a stream so assumed they had come from there.
We could hear them running in the roof and under the floor.
We had the council pest controller out, we did get a quote from a private company but in comparison the cost was extortionate!
BTW - I have two cats who did bugger all, we had tried putting them in the attic and extension ceiling. They are too pampered and lazy.
The council guy put poison blocks in the attic, under the floorboard in bedroom and in the extension roof.
He did advise what would happen, the rats would eat the poison, get insanely thirsty, leave the area to seek water and then die away from house (hopefully)
We stupidly blocked any and all access points as soon as we heard the rats in the house (before we had pest control) so unlucky for us, the rat did indeed die in the house. The smell was awful and first off we couldn't find the body, our JR x dog did a great job of indicating the approximate area. Hubby put a camera in the ceiling and we had to cut a hole in the ceiling to get the bugger out.
Touch wood, never had any problems since, although I do still spot the odd live rat in the woods when I'm walking the dog.
The council use industrial stuff and offer re visits in our area so you should be fine, if it wasn't for the dead body it was dealt with mostly quickly and easily.