Sex in the City: Down in the Edinburgh fettish dungeon

'We left the kids at home in the Borders and just popped up for the night," says Moira, a mum-of-two in her mid-forties, dressed neck-to-toe in a leather catsuit.

"It's a lovely venue and great to see everyone again," she adds in passing.

Her husband, Dave, a 6ft 3in bear of a man, who is wearing "ass-less chaps" and a leather waistcoat, asks us: "It's looking like quite a good turnout tonight. Is this your first time?"

Unchartered territory didn't even begin to cover it. Clearly a pair of 24-year-old flatmates, pretending to be a curious professional couple in their late twenties, had already stood out after two minutes at the city's monthly DV8 fetish club.

Moments earlier, back on street level, one of the underground night's organisers, a heavily built Fifer who introduced himself as Footman John, had already apologised for being hesitant over allowing us along.

"You can't be too careful. You've got to be wary of these press b******s, they've tried some stunt in Glasgow before," he snaps resentfully.

Usually the monthly club only allows regulars or those that can be vouched for by several members, but John has allowed us to enter after a brief meeting in the near deserted traditional working man's pub upstairs.

"God, yeah, b******s," we say, as my flatmate Lauren and I nervously look at each other.

Wasting no time, the 45-year-old explains casually that he would like to stick his nose in between her feet at the first available opportunity.

Making our excuses we descend into the "dungeon" below, but only after agreeing to the dress code: revealing dresses for women; PVC, leather or bare chests for men.

• Mystery of the drive behind unusual sexual desires

As we enter the dingy basement in the city's West End, an 18-stone woman is bending over an old school gym vaulting horse, her bare backside exposed, being flogged by a stocky man with a greasy blonde ponytail brandishing a cat o' nine tails.

On a nearby table is a selection of whips, chains and cuffs.

Shortly after we arrive at 8.30pm, several couples begin to strap each other to a large St Andrew's cross in the middle of the bare-walled cavernous room, big enough for 60 people.

The basement is below a locals pub not known for its welcoming atmosphere, but with its separate entrance and own bar, everyone outside the "dungeon" door seems oblivious to what goes on below.

As we sit around the edges chatting to other couples, another organiser, a 44-year-old woman from Dundee, leads a man, naked apart from a leather gimp mask, on his knees to another vaulting horse and shackles him into place.

Wearing a Soviet army green tunic and a huge officer's peak cap bearing the hammer and sickle, with leather hot pants and lace tights, the woman attaches a metal clamp to her "victim", eliciting a scream that barely causes a batted eyelid.

"That's Mistress Feral," says Hannah, the 18-stone woman from the start of the night. "She's brutal."

As time passes, the sound of whipped leather, giggles and moans fills the air. The scene is not unlike that from Stanley Kubrick's Eyes Wide Shut, but with a less attractive cast.

Later, we meet Jenny, a glamourous dark-haired 21-year-old Queen Margaret University student, dressed in a basque corset and skimpy French knickers, and Charlotte, a pretty blonde primary teacher in her late twenties, wearing a revealing lacy bra and pants, who trekked down from Aberdeen for the night.

As they circle the room, two men pass, one whose belly hangs from an all-in-one PVC catsuit. So what attracts two single young women to a dingy fetish club? "My friends don't know. I'm not exactly sure what they'd think," says Jenny. "I like the atmosphere, it's welcoming and you're assured of a good time.

"It's hardly like it's a sex club," she quickly adds.

"I don't usually get that involved. Just once at the Glasgow night I got strapped up and spanked. I have to admit it was good fun, but only because I felt safe and was ready for it."

Primary teacher Charlotte adds: "I wouldn't have come if I hadn't met Jenny. I met her on (fetish social networking site] Fetlife. We just thought it would be a good time."

Alongside Jenny and Charlotte is Helmi, an Edinburgh Napier student wearing a see-through dress over underwear, who arrived in the Capital just two weeks earlier from her Scandinavian home.

"My boyfriend doesn't mind at all. We used to enjoy going to these kinds of nights all the time back home," she says.

With just an hour-and-a-half before the night ends, the ferocity has increased and inhibitions are lost as the drink flows.

One unfortunate reveller in a full leather gimp costume hangs at an awkward angle from a chain in the ceiling.

Spectators look on as the "gimp" is spun around, with an unintended comic effect, while others caress each other's leather and PVC-clad bodies.

Making our excuses, we head back upstairs. As we leave behind the thwacks and screams, it is hard to shake the feeling that we are leaving a cosy club, where surprisingly normal couples, students and parents on a night out had welcomed us into the fold.

Some of the things we saw might not have been out of place in a torture scene in a Quentin Tarantino film, but for a generation which has grown up on such fare - and much worse - there was nothing shocking or to make you want to turn away. It all feels uncomfortably normal.