Most owners have feed their pet food that is potentially harmful to them, such as leftovers, fruit and milk.
A survey by the Co-operative showed that 91 per cent of owners treat their pets with foods they are not supposed to eat, which is costing £21.6 million in extra vets bills every year.
Nicci Townley, Pet Food Buyer at The Co-operative, said: "Owners need to be aware that feeding pets the wrong kinds of foods can be dangerous.
“Owners wanting to care for their pets properly should feed them with nutritionally-balanced pet food to keep their faithful friends fit and healthy and only feed them specially formulated treats."
Research showed that 12 per cent of owners feed chocolate to their pet, despite it being toxic to animals.
It also revealed that 35 per cent of owners feed leftovers to their animal, even though it can be dangerous for animals because it may contain too much salt and sugar and is not nutritionally balanced.