RAT infestation...UK please?

We found a dead rat on our lawn the other day...so I got paranoid we might have rats in the garden nesting somewhere...then I remembered that there was a rabbit hutch at the bottom..near the fence that was covered in undergrowth (no rabbits)...the fence backs onto a railway track with LOADS of undergrowth...so tonight I banged on the roof of the hutch and heard a scuffle and a faint squeak...so I probably have rats! How do the rat catchers deal with this? How do they get rid of them? Do they poison the poor rats and do I then have to deal with their bodies? I am an annimal lover but I have 2 small children...so the rats have to go.......