I read this post right after I saw a news report which claimed the borough we moved from last year now has the 6th largest population of rats in the country. I'm darn' glad I'm outta there although I never saw a rat. Someone told me that was because we had so many urban foxes, which keeps numbers down.
However, a friend whose house was invaded by rats had to use a pest control company who came and put traps down. They wouldn't use poison because of the danger to my friend's and other cats. She was also told to replace the broken airbrick under the kitchen floor, which was where they gained access, and to check all her other airbricks were intact. She was also advised to cut back overgrown shrubs and jungly weeds in the garden so there was nowhere for them to nest; not to scatter bird seed on the ground and to make sure rubbish was in a securely lidded bin. I think she would happily have napalmed the garden if it meant the rats stayed away! I think a total of three rats were caught in the traps over 2 to 3 weeks and since then, there's been no further problems. I think the total cost was around the £200 mark in the spring of 2016.