The affluent Home Counties in the UK seem to be grappling with a strange problem of rats, estimated to be around 80 million in the United Kingdom. The rat poison is not working as the rats have developed resistance to the poisons presently in use. The rats have genetically mutated and are breeding very fast. Poison manufacturers sought permission to use brodifacoum, a powerful poison to control this menace.
Graham Chapple from Newbury-based Rapid Pest Control said "The recent wet weather and flooding we've had has seen them pushed out of the sewers and we've had a lot more calls about people seeing rats in the loft or spotting them during the day, which used to be relatively rare.They're just looking for somewhere safe to do what rats do, which is breed prolifically.The mutations seem to be spreading reasonably quickly and I know they are having problems in Birmingham, Scotland, Hampshire and other areas. It is not so much that brodifacoum is a stronger poison, just that the rats haven't developed resistance to it, so it will be much more effective."
Source-Medindia