We have rats too. One ran over dd and my feet this morning - right outside our front door!
Your council will probably use contractors to come and kill them (They put down baited boxes). In our area it costs £51 - or £15 if you are on income support.
Our council also said how to do it myself. You have to make a little tunnel and put a bowl of rat poison (from any good hardware shop apparently) in it. You fill it up every day until none is being eaten (then it is asumed the rat is dead). We know where the rats are living so I'll put the tunnel there (has to be big enough for a fist apparently).
If you don't have a roof to the tunnel, the birds will eat the poison (apparently it doesn't kill them).
Anyway good luck!