I stripped for Spencer Tunick

I would like to think it was my passion for the arts that led me to strip naked with 150 strangers and jump into a heated swimming pool on a rooftop in east London. We were the volunteers who had agreed to be photographed by the (fully clothed) artist Spencer Tunick for his latest "live" installation.

But as I bobbed among the swell of naked bodies, I wondered if this was art, pornography, or just rampant exhibitionism. Whatever its definition, I had disrobed on the roof of the private members' club Shoreditch House, a former warehouse, at about the same time that most of the country was preparing for bed.

If a breakaway faction among us had not been orchestrating a high-spirited "Mexican wave" in the water, then this baroque, voluptuous vision of nudity might have passed as a scene from a modern-day Fellini film. But this was Britain, and we appeared to be doing nudity with Benny Hill sniggering, comical tan lines and plenty of plonk.

Tunick, the American artist best known for creating "epic" sculptures around the world involving up to 18,000 people at a time, photographed in precise formations, had scaled down the numbers for his latest project.

In recent times, he has been working on his "Party Series", which attempts to recreate Renaissance-style paintings in modern settings. He hopes to exhibit the result in about two years.

"This is about nudity that takes places in the context of a party," he said, before the shoot on Thursday night. "It's about the bodies; shapes that are sensual but not overtly sexual. For some, it's a party climax, but I want the party to continue after I go."

While at times it may have felt closer to Carry On than Cara-vaggio – with some last-minute changes of mind ,leaving several men clutching their modesty – there was a Bacchanalian spirit of rebellion and revelry in the air.

Only half an hour earlier, we had been a roomful of nervous strangers signing consent forms and pondering the terrors of total exposure. Guests, among them entrepreneurs, headhunters, artists and lawyers, were offered plenty of complimentary wine. Yet, despite the Dutch courage, there was still a moment of panic when Tunick asked us to strip.

One moment we were making polite conversation about the cold air, the next we were propped up against each other's buttocks, lying intertwined on the floor, as requested by Tunick. Surprisingly, a few who had been slow to disrobe suddenly appeared body-confident as they strode to centre stage; some danced, others struck a pose. Only the minority crept around the edges, with hollow-eyed expressions.

As I took off the final items of clothing, the warning words of Stephane Janssen, a 72-year-old from Brussels who had featured in 11 previous naked sculptures, echoed loudly in my mind. He said Tunick, now his friend, could be exacting. "He has an idea of how he wants things. If you have a tattoo, you might be sent to the back. The same for a big butt." I braced for the worst.

Tunick, who was inspired by the 1960s artists staging public "happenings", said: "I enjoy seeing the change in people's spirits when they are naked, their enthusiasm to go beyond their limits, shedding their clothing. I like working with people who have a new outlook for a short period. It also feels like taking colour off a canvas and starting over again with white."

Naked ambition

Spencer Tunick, 41, began photographing unclothed individuals and small groups in the late 1980s after graduating from art college in Boston, Massachusetts. He progressed to organising massive human sculptures to emphasise the abstract rather than sexual side of naked bodies and has created more than 75 temporary installations, each with hundreds or thousands of naked human bodies in public locations all over the world, including Mexico City, where 18,000 people posed in 2007.