“After a hard day at work [devotees of puppy play] might come home and put on a puppy hood to get into the ‘headspace’ of just being silly and playing around or chasing a ball,” he says.

Once secretive and mainly practised by young gay men, this “lifestyle hobby” is believed to have started as a form of sexual domination in either Germany or the United States. Having evolved to place a stronger emphasis on non-sexual fun, it has gained adherents thanks largely to online networks and a greater social acceptance of “kinks” and fetishes. In the past few years it has also gained some prominence at public events such as Pride marches.

The new guard includes people like Chip, a heterosexual 48-year-old caterer and father of two from the sedate town of Guildford, southwest of London, who spends much of his leisure time as a rottweiler.

Chip, who wears a £300 (HK$3,000) leather hood, is the “alpha” or top dog of his pack, which includes two gay men, Oryan and Fidget, and two straight women, Chip’s wife, Biscuit, and 23-year-old Pepper, from Ashford, in Kent.

“It is just a fantastic release,” says Chip, after he and his wife have spent much of a weeknight evening scurrying around the floor of the family living room on their knees and knuckles. For 90 minutes, they barked, growled, nuzzled each other and fought over squeaky toys while their two teenaged sons kept themselves busy in their bedrooms, upstairs.

“I have been interested in puppy play for 15 years; it is amazingly liberating when you get into the headspace of a pup and just act on instinct,” Chip says. “I normally need to be responsible and in control all the time but as Chip I am mischievous and playful and bouncy.”

Some pups describe that “headspace” as a form of meditation.

At one stage, Chip breaks off our conversation to chastise his 18-year-old son for going out on a hot day without sun­block. It is a normal parental lecture except the dad delivering it happens to be wearing a black lycra bodysuit and a gently wagging tail.

While many pups use “insertable” tails and others wear tails that protrude from their belts, Chip prefers a tail connected to a harness hanging below his belt.

Pepper, who is an “omega”, or junior, member of the pack, says Chip has become “a second father” to her since she became a pup this year. Like many pups she has a handler, her flatmate and former boyfriend, Rich, who plays fetch with her favourite toys, rubs her belly when she is “good”, lets her up on the furniture when he is feeling indulgent and looks after her on public outings.

“The main thing I have to do is make sure she has fluids because pups forget to drink,” says Rich, a 36-year-old ware­house manager, as Pepper frolics around their small flat yapping and panting. “Her being a pup is calming for her and a joy for me because I get to just play and have fun instead of worrying about normal problems and pressures. But I don’t know where she gets the energy. As Pepper she is tireless.”

Pepper eventually joins the conversation. “As soon as I stand up, the headspace just pops like a balloon,” she says. “As a human I have Asperger’s and attention deficit disorder and a lot of people find that overwhelming. But as Pepper I can bring that side out and people like it. It is astonishing how naturally it comes. A lot of people think it is acting or pretending but it is not. It has to come from within and that is how I get so deep into the headspace.”

When Wignall, a PhD candidate in cultural studies, published his academic paper last year, the lack of previous research left him unable to say when, where or how the prac­tice had developed. Dr Jamie Lawson, an anthropologist and teaching fellow at the University of Bristol, is following up Wignall’s report with a research project that is “trying to understand more about this behaviour and what people get out of it”.

“It involves casting off your humanity and surrendering some power by giving up things that make you human, like speaking, walking on two legs and even being able to use your hands,” he says. “The question is, why would they do this? The simple answer is they enjoy it, but that’s actually very complex and it is worth looking into.”

Wignall’s paper noted that most puppies prefer to keep their pup play secret from their “non-pup” friends, to avoid awkward questions from family and employers. But Ian Dinev, a 20-year-old computer gaming student at the University of Birmingham, is quite open.

“I always walk around at uni in at least a collar and most of my classmates know by now that I am a pup,” says Dinev, who can remember barking and imitating dogs as a small child growing up in Bulgaria. “When I told my mum I was into puppy play, she said, ‘That explains why you used to chew up things’. It is just part of who I am. I have had strangers shout at me in the street about it but I’ve never been physically harassed.”

The anonymity of a hood helps most pups find the liberating headspace they crave. Dinev spent £200 of his Christmas gift money last year on a customised grey and black wolf-style hood from a US website. His leather harness was £40 on eBay, his “paws” are boxing gloves from a sports store and his insertable tail was a second-hand gift from a friend.

Scamp, or Alex Clark, a 32-year-old bicycle repairer from London, and his handler-boyfriend, Andy, an artist, are also happy to reveal their identities. Scamp has been doing puppy play for 15 years, and for six years often slept in a dog cage in his bedroom.

A 28-year-old friend of his, though, does not want even his “pup” name to be published, as he suffered a backlash in his job – working with vulnerable children – after informing his employers of his hobby.

“I have to tread carefully but the truth is that pup play is completely non-sexual for me. It is about escape and play because, when you are in the headspace, you are instinctive and thoughtless, you just act on whatever comes into your head.”

Alpha Archie, a 24-year-old who works in marketing for an Islington sex shop, also declines to be photographed without his hood.

“The anonymity of the hood is quite liberating and not everybody knows I enjoy this,” he says. “I spend more time as a handler than a pup but I have many kinks and this is just one. It is hard to deny there is a sexual side to it but I think a lot of people are in it for a sense of belonging and affection.”

Hexyc, a physics graduate who recently landed a job at a London finance firm, says he worries that employers and workmates might make harsh judgments about his dual life: “I’m open with my friends about it but I’m only 22 and I could regret it later on if I went public.”

Hexyc designed his own bright-blue rubber suit, which is emblazoned with coloured hexagons and epitomises the shift of puppy play from black leather to something more playful and expressive.

Putting the suit on is a tiring exercise that takes more than 30 minutes and begins with slathering his body in lubricant. Next come a chest harness, collar and dog tags, a latex puppy bandana, heavy-duty kneepads and bright green boots. Finally he needs help to zip on his paws, which lack thumbs. That robs him of a lot of independence, which is part of the attraction for those who enjoy not being in control. Hexyc also has his own leash, dog bowl and lots of toys, including balls, chew rings and play sausages.

“People are into it for different reasons. For some it is all about sex, for others it is just fun and not at all about sex and, for most, it seems to have elements of both,” he says. “I would not pretend that there is absolutely no sexual attraction to it for me – right now I am wearing a dog collar and a rubber suit, after all – but I mainly do it for fun. It is about being silly and affectionate, enjoying unconditional love and not having to think about all the things that worry human beings.

“Sometimes I just curl up at my boyfriend’s feet for a couple of hours while he watches a movie or does some study.”

Female pups say they suffer a backlash from gay men unhappy with their involvement, and many pups say it is a “bitchy” community as different factions try to define puppy play to suit their own tastes.

Public appearances can be awkward, with one experienced pup saying that “older adults and little kids are great but you can get some aggro from teenagers ... and from real dogs”.

That is borne out by trips with Chip to a large park near his home and with Scamp, his handler Andy and another pup to a park in Croydon, south of London. Bystanders smile quizzi­cally and occasionally shake their heads in disbelief but generally take a “to each their own” approach.

“They’re not hurting anyone,” shrugs Andrew, a 51-year-old bank worker who was stopped in his tracks by the sight of Andy and his pups. Several real animals – called “bio-dogs” by human pups – bark madly at Chip, who has perfected many canine growls, postures and other mannerisms.

The rapid growth of puppy play has, over the past two years, seen most major sex shops in London devote sections to puppy hoods, collars and other trappings. At Clonezone in Earls Court, store manager Rafal Liszewski says demand has reached the point where he recently employed “a pup” to help deal with puppy customers.

Social network puppypride.co.uk has 1,500 UK-based members, according to London-based web developer Kye Etherton, who puts 40 unpaid hours a week into running it. “We are the most active network around but we obviously would not have every pup in the country, so my estimate is there are something like 10,000 in Britain,” says the 28-year-old Oxford University graduate.

Others say 5,000 is a more realistic estimate but the rapid growth in recent years has been evident at the annual Pride in London march. The first pup involvement at Pride was six years ago, when Etherton, who is a handler, walked with five pups: his boyfriend and “four strays”. Last year’s Pride featured 85 pups and handlers and this year there were 150.

There are also regular events in nightclubs and other venues featuring “mosh pits” where pups can play together, sometimes with a heavy sexual element and sometimes just rolling around like puppies.

According to Etherton, the US has more pups than Britain and there are active communities in Germany, Belgium, the Netherlands and Australia.

“Tokyo has about 20 pups, there are some in South Africa and there are two in Hong Kong, but one of them is emigrating to England later this year,” he says.

“It is very rewarding being a handler and playing with pups but it is obviously more fun being a pup so they outnumber handlers by about 20-1 and that is becoming a huge problem. We don’t have enough people to look after them at events and they can’t look after themselves because they have no hands and they are generally really silly. You have to make sure they drink plenty of water and don’t get hurt – it is easy to damage your knees and you can hurt your spine from adopting the wrong posture.”

Etherton once had to deal with a puppy who suffered concussion after being hit in the head while playing fetch Frisbee in a park.

While he is open-minded enough to welcome women and straight men into the pup world, Etherton is a stickler when it comes to tails.

“A tail is supposed to come out of the base of the spine but a belt sits a couple of vertebrae above that. When you see someone dressed as a pup with their tail sticking out that high it is just wrong – it looks silly.”

He is hoping to market his own insertable design, which “is more comfortable than any other tail on the market and wags better with less effort”, he says. “It will be made in the UK from top medical-quality materials – non-porous, sterile and non-allergenic.”

Zentai Spot, a 32-year-old theatre technician from Hertfordshire, north of London, who wears an elaborate full-body Dalmatian suit, is something of a celebrity in Britain’s puppy world. He was named Mr Puppy UK 2015, the first time the title was awarded. He got into puppy play 14 years ago through a fetish for skintight clothing and sought tips from the first book written on the subject, Woof! (2003), a US publication reflecting the old guard, heavily sexual and bondage-based understanding of human pups. A 2015 book, Bark!, better captures the new vogue for “playful fun”.

“I used to be the only straight guy at a nightclub event, but it is broadening out every day and the growth is coming from the soft side rather than hard-core stuff,” says Spot, whose human name is Tom.

He has spent more than £4,000 on his gear but says it’s “an affordable fetish – a leather fetish can be very expensive to start but, with pup, you can start off with just a collar”. Spot, who occasionally sleeps in a dog cage, has used a blog to advise younger pups such as Pepper on how to find the right head­space, making him a hero to many.

His former fiancée, Rachael, says she broke up with him over his pup obsession in 2008 because she was overwhelmed by it. But she believes if it had happened now, when there are more people to talk to about pup play, she could have coped and their relationship would have survived.

“We both regret the break-up now,” says Spot.

Spot and Rachael are still close, but he is now in a “friends with benefits” relationship with his male handler and flatmate, Colin.

Some pups admit to social anxieties and mental-health issues – “I honestly think some of these human pups could benefit from therapy but, unfortunately, they’re not allowed on the couch,” comedian Richard Osman has quipped – but forensic psychologist Dr Vincent Egan, of the University of Nottingham, says it is wrong to assume pups need help.

“There is an awareness now that what was once seen as disturbed and perverse can just be people expressing their sexuality or relationships in different ways.One generation’s perversion is the next generation’s normality,” he says.

“There are people who are neotropic, meaning they go towards trying new things and testing out boundaries in their lives and I think that is a big part of this. Some people ‘escape’ with a glass of red, some kill aliens or chase Pokémon and some do this. It’s a shame people can’t be affectionate, playful and silly without having to dress up in a PVC dog outfit but, if that works for them, then good luck to them.”