Roo has no problem with people. He just detests other dogs, particularly Jack, a fellow Jack Russell, aged seven, who shares the same home.

“Roo was fine until he was 10 months old when one day he started a vicious fight with a biscuit wrapper,” his owner, Lisa Morley, says. “I had a frenzied Roo suspended in the air with one hand while trying to fend off a furious Jack.”

The three-year-old Roo took out his aggression on other dogs too. “I have to keep Roo and Jack separate inside the house and I pay 10 an hour to walk Roo on a lead at set times in a controlled area with no other dogs around,” Morley, who lives in High Wycombe, says.

The PDSA animal wellbeing report last year found that 63 per cent of vets had seen an increase in dog-on-dog attacks in the past two years. It is against the law for a dog to be out of control in a public place or even in your own home, which includes attacking another animal. An owner can be fined, jailed for up to six months, or both. If your dog attacks a person or assistance dog the penalty is more severe. The animal can be destroyed.

Aggression in dogs is often related to fear, but can also be due to pain from a medical condition. Having established that Roo’s problem was not medical, Morley’s vet referred him to a behaviour counsellor, Kris Glover, founder of Reading-based Pets in Practise.

After a consultation, Glover attributed Roo’s aggression to a fear that Jack and other dogs would take his food. “Roo is a rescue dog so may have been the runt of the litter and unable to get food, or an only puppy not used to competition for food,” says Glover.

She introduced Roo to her stooge dogs, which are stuffed animals with real dog scent. The idea is to film a dog’s reaction so its owner can recognise warning signs. “The stooges are so realistic that one dog tore the nose off a stooge terrier. Another tried to mate with a stooge labrador,” says Glover. Roo takes one sniff at a stooge, realises it is a dummy and turns his back on him.

Glover accompanies Morley and Roo on a short lead to a public park to observe his reaction to other dogs. When he spots one, Roo goes stiff with his ears back and strains on his lead. Glover’s plan is to recondition Roo so he does not feel threatened. Each time he spots a dog Morley is instructed to throw a tidbit. “Roo wants to be friends with other dogs but is too scared. We want him to associate other dogs with something good and to realise they can’t get his food,” says Glover.

A golden retriever and then a spaniel, both off their leads, bound up to Roo, who spirngs into attack mode. Glover deduces that Roo has a comfort zone of just 5ft. The next step in Roo’s treatment will be for him to walk with a group of other dogs on leads who stay outside that zone. He will be thrown tidbits to reinforce the message that other dogs can be fun.

Fear-driven aggression can be averted if a puppy becomes familiar with other dogs at an early age. Preventing fear-driven aggression in puppies is crucial, and one effective method is early socialization with other dogs. The key to success lies not only in interactions with other canines but also in how the puppy behaves in its home environment. Introducing a puppy to various social situations and allowing positive interactions with other dogs from an early age can help build confidence and reduce the likelihood of fear-based aggression. It’s equally important to look out for signs of discomfort or anxiety in your dog, such as their sleeping positions, as this can reveal a lot about their emotions and whether they’re feeling safe and comfortable. Understanding what your dogs sleeping position means can provide valuable insights into their behaviour and emotional well-being, contributing to a harmonious relationship with your furry friend.

The PDSA report found that 89 per cent of vets think training should be compulsory, but that 60 per cent of UK dogs never get any training as puppies. Caroline Clark, an animal behaviour counsellor who runs Yorkshire-based Pet Education & Training, said: “An important time for puppies is around 4-12 weeks of age when they are at their most sensitive for learning. If they have not been exposed to a range of different situations they may be more fearful later on.”

Counsellors are also seeing an increasing number of aggressive cats. In many cases this happens because many cats do not spend enough time outside – known as misdirected predatory aggression – which has been made worse by the trend for indoor cats. According to the PDSA, 24 per cent of UK cats live solely indoors.

Lisa Morely, left, and Kris Glover with Roo during a walk in the park

Penaran Higgs, a pet behaviourist who owns Pet Shrink in London, said: “The happiest cat is one who comes and goes when it likes, has a big pile of dried food and not too many other cats in the area. Outdoor cats spend six-seven hours a day hunting.”

Shamik and Anushka Somia consulted Higgs after their indoor cat, Billie, aged two, started attacking them. “We’d come home and stroke him and he’d be happy, then we’d pick him up and he’d bite us or clamp down with all four limbs. He’d feel the urge to attack any exposed flesh with his teeth,” Shamik, who lives in London, says.

Higgs diagnosed predatory aggression, but also play aggression where a cat is petted for too long. She advised the Somias to let Billie decide when he wants to be stroked, to keep petting sessions short and not to pick him up. They also reduced stress levels by making Billie hunt for his food and creating more areas for him to explore. Games, TV programmes for cats and bird tables outside the window are good ways to stimulate an indoor cat.

Clark says owners must investigate the character and needs of a species before buying it as a pet because an owner’s own behaviour is sometimes to blame for aggression.

“Parrots bond with owners. I’ve had owners who feed a parrot mouth to mouth so it sees the owner as its mate. Then their spouse walks in and the parrot attacks because it sees them as a rival,” Clark says.

Consultations with a behavourist can cost 175- 250. Insurers may reimburse fees if the specialist belongs to a recognised body such as the Association of Pet Behaviour Counsellors.

Whether aggression can be cured or just managed depends on the pet, the owner, the cause, and how long the behaviour has existed. “A lot of clients see us as Crocodile Dundee. They expect us to wave a magic wand and totally change the animal,” Clark says.

Morley is more realistic. “I’ll never be able to let Roo off the lead but I think in time I’ll be able to walk him in parks on a long lead. That would be wonderful.”