People who dump fast food leftovers on the street are being warned they are encouraging a new breed of super-rat.
The campaign group Keep Britain Tidy said snacking on half-eaten chips and burgers means the rodents are getting bigger and more energetic.
Even dropped apple cores, banana skins and bread crusts left out for birds are adding to the rats' food festival.
There are about 60 million rats roaming the streets of Britain. The critters can fit through a gap of just over 1cm.
The brown rat is the most common UK rat
They weigh about 335g
They are 200-270cm
They can jump 70cm
Experts put the growth of the super-rat down to the fact the creatures are now eating more food with lots of protein in it, and fewer carbohydrates, which means they have stronger muscles.
The number of food scraps dropped on the street has leapt over the last five years and Keep Britain Tidy said the rodent problem will get worse if people don't clean up their act.
Anyone caught dropping litter in street can be fined £80 on the spot.