Why Princess Diana's Niece Lady Kitty Spencer Slept on the Street in London

"We were completely safe, while the young people on the streets are vulnerable and in danger," Spencer tells PEOPLE

Photo: Andy Barnes/Centrepoint

Lady Kitty Spencer slept on the street last week —but she is quick to note that her experience was nothing like that of the homeless youth for which she was raising awareness.

“The sleepout doesn’t replicate the homelessness,” she tells PEOPLE of her experience on behalf of the charity Centrepoint last Thursday on the chilly ground near the River Thames in London. “We were completely safe, while the young people on the streets are vulnerable and in danger. It is a completely different scenario.”

“This was about giving people a glimpse into this reality and enforcing just how difficult the situation is that these people find themselves in,” adds Spencer, 25, the eldest daughter of Princess Diana’s brother Charles Spencer, and his first wife Victoria Lockwood.

“It was cold and uncomfortable to sleep on the ground and everyone was cold to the bone,” says the Centrepoint ambassador, who wrapped up in “layers and layers” for the night along with a group of fellow supporters. “That, for me, wasn’t important at all. We knew we were doing it for one night and psychologically we knew we weren’t in any danger at all. We knew that we could go home to bed and bath and a meal, while these young people don’t have any of those things – and that would be day after day.”

Spencer’s cousin Prince William, who followed his mother Diana in championing Centrepoint, also slept out for the charity in 2009. (Spencer has a rule not to talk about her family in interviews.)

This year, Spencer — who grew up in South Africa but has now settled back in London, where she is building a new career under Storm Model Management — and her friends were joined by actor Matt Barber of Downton Abbey, who led a karaoke-style singalong. Actor Christopher Biggins even read a bedtime story.

Andy Barnes/Centrepoint

Spencer notes that 26 percent of young homeless people have stayed with a stranger, while 9 percent have harmed themselves so they can be taken to the emergency units of hospitals for a safe haven and a bed. “When I was lying there falling asleep, you feel angry that this is such a crisis in 2016,” she says. “Mankind is so advanced and ahead of its time in so many ways, but you think how could so many be living without so much as a room or a bed to call their own.”

The sleepout nationally raised about $500,000 toward the charity’s Christmas Appeal, which can be donated to here.