The latest study carried out by Simon Wheeler, head of marketing for insurance firm Pet plan, showed that a quarter of all pet rabbits are overweight, with eight out of 10 vets warning that the trend is escalating.
It was also found that the reason were the owners, who are giving treats such as honey and chocolate. Even carrots was also found top be contributing to the problem, with many varieties grown for their high sugar content to make them sweeter for human tastes.
The survey conducted by vets is the first of its kind and underlines Britain's growing problem with fat pets. Obesity in rabbits is rapidly approaching the same levels found in dogs and cats, of which about one in three are obese. Some rabbits are twice their recommended body-weight.
During the survey, it was found that increasingly, pets now live indoors as "house rabbits" rather than hopping around the garden, while vets say even outdoor rabbits are often kept in hutches that are too small and so they don't get enough exercise.
Richer processed pet foods are also being blamed for the problem.
Rabbits find it harder to lose weight than cats or dogs, and the trend has prompted the Rabbit Welfare Association, the British Small Animal Veterinary Association and the People's Dispensary for Sick Animals (PDSA) to speak out about the considerable health risks associated with obesity.
Two of the country's largest pet insurers say obesity-related issues now make up 25 per cent of claims for rabbits, which have increased in popularity in recent years. Up to two million are kept as pets.
"The number of obese rabbits I see in the surgery is only the tip of the iceberg. If you are feeding a rabbit toast and honey, that is a lot of calories for them and will pile on the pounds," the Telegraph quoted Elaine Pendle bury, a senior vet at the PDSA, as saying.
Adult rabbits weigh between 1kg and 8kg, depending on breed.
However, Judith Brown, veterinary executive of the Rabbit Welfare Association, said it was now common to see rabbits more than 20 per cent over their ideal weight.
Among the breeds particularly vulnerable are continental giants, which can grow to the size of a small dog. They were once bred for meat and can very quickly put on excess weight.
Fat rabbits can find it difficult to clean themselves and this may lead to an infestation of maggots, which can be fatal. Obesity can also lead to a condition called "sore hocks", involving painful wounds on the paws, which can also cause death.
It can lead to joint and bone problems, heart and breathing difficulties, and an increased risk of cancer.
Wheeler said that 25 per cent of all claims for rabbits related to dietary issues or obesity, up from 12 per cent last year.
"The results of the survey suggest rabbits are catching up with the nation's cats and dogs in the obesity stakes. It's serious in all pets, because being overweight can lead to heart problems, diabetes and respiratory problems," the Telegraph quoted him, as saying.