I had rats in my loft last week. I could hear them running around at night right above my bed, its just a plywood ceiling so it was very loud and somewhat disconcerting.
I called the council who sent around a man who put some poison in the roof (and charged £35 for this, I sure it used to be a free service) Apparently its illegal for a non-licenced rat catcher to use professional grade rat poison, so no chance of a diy job.
Anyway, it seemed to do the trick; that night the rats were extra lively, perhaps driven mad by the poison. The next night they were silent.
A more ERE solution though might be to borrow a cat. I heard of a women whos rural house was invaded by rats. She borrowed a suitably assertive cat, which proceeded to brutally slaughter them all. It left a mess but dealt with the problem.