The Italian girl with the pixie haircut stares at me with wide, serious eyes. "I'm into the usual stuff – latex, whipping. But you know what really turns me on?"
What? I ask.
"Oh yeah. I have a collection."
She looks at me pityingly.
"They don't have to be perfect. As long as there's a swastika I get a wide-on. I'm not some kind of weirdo, you know."
We are standing on the upper deck of a river cruiser on the Thames. It is currently heading towards Canary Wharf at a good clip. Around us are a group of men and women, mainly middle-aged, in varying states of undress. As this is London's premier, annual, on-water fetish party, most of them have squeezed their now less-than-pneumatic bodies into latex, rubber or PVC.
Despite the Nazi fetish of the Italian guest, the party is encouragingly inclusive and diverse. From where I'm standing, I can see a jacked up black guy in a white leather skirt, an old white fella in a school uniform – grey shorts, tie and prefect badge – and a Middle Eastern dude in a green rubber corset licking the (possibly fake) Louboutins of his giggling lover. Every so often, when another boat passes, the fetish-clad denizens clap and wave and cheer as bemused tourists and out-of-towners stand and stare.
"The Boat", as the event is called, happens every June. It's been going for the last 22 years, longer than Torture Garden or any of the capital's other kink parties. Setting sail from London Bridge Pier, this vessel of flagellation enthusiasts travels up and down the river until 2AM, going as far as Greenwich in the east and Putney in the west. According to its website, the shindig is run by "The Firm", a "shadowy politico-criminal organisation".
Intimidating as this sounds, when I board I am welcomed by organiser Noah, a grinning chap in leather, and Jacko, another official, who wears a Dickensian frock coat and looks more like a town crier with a penchant for six-pint ploughman's lunches than an urban outlaw.
On board, a bloke named Phil with wispy grey hair and a maid's outfit offers me a tray of cold meatballs in curdled tomato sauce.
"I'm a service sub," he explains when I enquire about his get-up.
"You get off on serving people lukewarm foodstuffs?" I ask.
"I like to make people happy," he says. "If they feel good then I feel good too."
Is it a sexual thing?
"You bet," he responds enthusiastically.
The Firm's website extols the virtues of a good spanking beneath the historic raised walkways of Tower Bridge and many are relishing the opportunity. One guy in a top hat has a skinny older woman over his lap. He's giving her six of the best, his hands in leather-studded fingerless gloves.
"You're not telling me the truth," he says, his hand coming down hard on her dimpled and quivering butt.
"I am, master!" she squeaks.
The crowd is nothing if not friendly and even if you've come alone, as I have, the opportunity for a spot of nautical hand-to-panty fun is never far away.
"You can spank me if you want," the Italian girl I've been chatting to proposes. I politely decline, instead following her down to the bottom deck to check out the rest of the party. Here, I'm buttonholed by Derek, a claims adjustor from Catford. He's wearing a rubber corset and a latex gimp mask that makes his head look like a ball of liquorice.
It turns out Derek is keen to open up about his passion for auto-asphyxiation over the vol-au-vents that Phil, the service sub, is now hawking. "It restricts your breathing," he says of his shiny fright-suit. "That makes it fun when the missus is stretching out me ball sack, I can tell you."
Undoubtedly. How did he first get into this scene? "I loved the fetish magazines of the 60s," he says "John Sutcliffe's AtomAge mag. When I first saw a bird in head-to-toe rubber posing next to a cheese plant on a Formica table I almost shot me load right there and then."
Given the age of many of the participants here it's not surprising that there's a certain nostalgia for back-in-the-day kink parties. Brenda, a cross-dressing welder from Stevenage who clutches a pint of real ale in his huge fist, reminisces about famed London DJ Rubber Ron's mansion sex parties.
"There were people boning all over the place," he says, breathlessly. "After a good session they'd have to take all the curtains away for cleaning, what with everyone wiping themselves off on them."
Down below deck the party's really going off, with the happy flagellators letting go with abandon. The DJ drops Lil Louis's "French Kiss". "I want to see some spanking in time to this one," he bellows over the mic.
Everyone is happy to oblige. A cute girl in a kilt is thrashing her boyfriend, who is tied to a whipping frame. A lady with a blonde Pat Butcher crop is having her nipples flicked dextrously by a female companion. Another girl has been suspended from a pillar by her boyfriend, who is armed with a complex pulley system.
Meanwhile, others just dance. A woman in a black kaftan throws shapes to Madonna's "Justify My Love", while a skinny Marilyn Manson-lookalike in a leather posing-pouch shakes his arrhythmic thing. There's no outright sex going on, although I do spot the Italian girl performing a lethargic hand job on a stoned-looking bloke in Ray-Bans later on.
It's now nearly 2AM and The Boat will soon by docking, ending its sore-arsed odyssey for another year. But standing on the top deck, watching the iconic London nightscape slide by, I feel I am no closer to understanding why it's preferable to spend five hours smashing someone's butt on water rather than in a club or at home. But then I get chatting to cross-dresser and Boat old-timer Doris, a man in his fifties who wears fetching neon-orange hot pants and multi-coloured braids in his hair. As we talk, we stand watching a man romantically flogging the bare breasts of his girlfriend – who wears a fishnet body stocking – with what looks like a rubber baseball bat.
"It's like this," he muses. "Life is difficult for a lot of people. If they want to let loose thrashing one another to house music while floating up and down the river on a boat, then why the hell not?"
He has a point.
"Besides," continues Doris, "the motion of the water does strange things to me winky."
"And best of all, once you're on The Boat there's no getting off. Not for five hours." He fixes me with a steely look. "There's nowhere to hide."
Thankfully at that moment we dock. I say goodbye to Doris and head for dry land. As I leave, a cackling Noah pumps my hand warmly and thanks me for attending. In spite of their predilection for hitting one another hard with paddles and whips, the Boaters are a friendly crew. Al-fresco, water-bound, riding crop action may not be to everyone's taste, but given the increasing homogenisation of London's nightlife, it's heartening that the capital's spank-happy love renegades still have a place where they can party.
All names have been changed.
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