"I thought you were legally obliged to report rat sightings to the local authority. I certainly did when we had one and they sent someone round to deal with it. If I thought my neighbours were harbouring rats I would be horrified, as in no time at all, they would be on my property. They are vermin and need to be dealt with. Vile things!!"
Nope, no legal obligation, the councils would have no time to deal with anything else! I think that many councils now make a charge for vermin services unless you are on benefits. If you think that an area of land is a health risk then you can report it and the council will investigate and require action if your complaint is upheld.