People have been urged not to provide cat food for felines that come into their gardens unless they look underweight.
Battersea Dogs & Cats Home issued this advice after revealing that half of the cats in its shelters may actually have homes.
The charity noted that many cats brought to it are mistaken for strays because they are not wearing a collar, but said people should ask around their neighbourhood before bringing the cat into a shelter.
Louise Taylor, Battersea's lost & found assistant, said: "Cats can roam large areas in their neighbourhood and are notorious for befriending people for food even when they are being fed by their owners.
"We see too many cases of people bringing happy and healthy cats into us as 'strays' who probably have an owner somewhere."
She added that while the charity does not want to deter people from bringing strays in, the number of cats being brought in needlessly is putting a "big strain" on its resources.
Battersea suggests people who suspect a cat to be a stray take the animal to their local vets, where it can be scanned for a microchip.