Video: Yorkshire's fattest cat can't even fit in her basket (She's called Puff, of course)

The fat cat has been selected to compete against 12 other oversized pets, including dogs, other cats and even a rabbit, in the PDSA’s Pet Fit Club.

Tipping the scales at 1st 3lb (7.5kg), Puff has eaten her way to being 50 per cent over her expected size of 11 pounds.

The oversized white and cream kitty, who will pinch fish food from the tank if given the chance, was adopted by owner Marie Clair, 58, just over a year ago. When Marie collected her she was amazed by her sheer bulk.

She said: “Puff is the biggest cat I’ve ever seen. It was obvious her previous owners had overfed her and overdone the treats. She was even too big for the cat carrier so we had to use a dog cage to bring her home.”

Puff is bigger than both her dogs Eric, a Maltese terrier, and Ernie, a Poodle cross.

Ms Clair said: “She wasn’t very social, and in her first few months with us needed lots of coaxing, but she’s settled in now. I know she was quite stressed while living with her previous owner, which may have led to her over-eating or not getting enough exercise. Bowls of well-intended prawn treats wouldn’t have helped her weight either. But all that’s changed now. She rules the roost here and, because she’s so big, she bosses my dogs and other cat around. She knows her own mind and does whatever she needs to get her way!”

For the last 12 months Ms Clair has kept Puff on a strict diet and helped her shed around 5lb. But she still has a long way to go to reach her ideal weight of 11lb (5kg). She is currently at risk of long-term health problems including heart disease and diabetes.

she added: “I’m hoping Pet Fit Club will help us get Puff down to a healthier weight. I’m strict with what she eats but she’s determined – I’ve caught her eating the fish food from the fish tank before!”

As part of Pet Fit Club, Puff will embark on a strict six-month diet and exercise programme, specially tailored by the vets and nurses at Sheffield PDSA Pet Hospital on Newhall Road.

Joanne Smith, PDSA Animal Care Assistant, who will be helping to oversee Puff’s diet, said: “Pet obesity is a serious issue that affects millions of UK pets. Like humans, pets carrying excess weight are at risk from developing serious health conditions such as diabetes and heart disease. It can even shorten their lives.

“Marie has already done great work helping Puff slim down. Now, with the help of PDSA Pet Fit Club, we’re hoping to get her down to her ideal weight. We will support her every step of the way over the next six months to ensure they succeed.”

“If owners are unsure what to feed their pets, or are concerned about their weight, they should always seek advice from their vet.”

Puff will be competing against seven dogs, four cats and a rabbit, including Cilla, a crumpet-loving American Bulldog from Liverpool who tips the scales at a hefty 8st 8lb (54.4kg). Also taking on the six-month weight loss challenge is a rotund rabbit called Pebbles, from Blackpool.

PDSA Pet Fit Club was launched in 2005 and has already helped 74 dogs, 32 cats and six rabbits lose a total 63 stone 11lb - equivalent to over 400 bags of sugar, 6,500 tins of tuna, 7,000 sausages or four heavyweight boxers.