When Cat Deeley went on a night mission into the streets of Manila in the Philippines last month, Britain’s favourite girl next door was finally lost for words. “It was like . . .” she reaches around for a word. “It was like looking in the jaws of hell . . .”

Deeley, 31, had landed in the island nation to spend a week observing the awful lives of its 250,000 street children as part of Unicef’s charity football match Soccer Aid, which takes place this afternoon. The match consists of celebrities (Gordon Ram-say, Alastair Campbell) and former players (Alan Shearer, Luis Figo) taking to the pitch at Wembley stadium to raise money for deprived children.

When Unicef first tried the concept in 2006, it raised £2.6m. This time round, Ewan McGregor, Orlando Bloom and Deeley have been drafted in to show Unicef’s work around the world. Deeley found herself leaving the glossy Los Angeles studio of So You Think You Can Dance, the outrageously successful talent show she presents to 19m Americans every week, and flying to the Philippines.

“I landed at something like 5 o’clock in the morning and we went straight out onto the streets. We were slightly mad to do it as there can be a security issue. It’s full-on – the poverty and pollution are beyond extreme. You can’t imagine what these kids have to go through.

“One night we went out and it was pitch black, the thunder and lightning started, then the torrential rain came in. I squinted to try to see what was concrete, what was rubbish, what were homes, what were people, what were limbs, what were rats. I looked down and saw a pile of rubbish, then realised it was a house with two baby girl twins sitting naked at the door.”

Homelessness is an epidemic in the Philippines, with people driven to the cities on the promise of work but finding little or no support structure when they can’t make enough to live on. Parents, who often don’t have even a basic education, struggle to look after themselves let alone their children, so the kids run wild. And they’re the lucky ones. Many of the children are runaways or – even sadder – have simply been lost.

The attendant problems are as predictable as they are devastating. The majority of kids are addicted to glue (they call it “Rug-by” after a brand of cheap glue), crime and human trafficking are rife and both girls and boys fall into prostitution.

It’s worse at night, says Deeley. “I met a boy called Alturo, who was 14 but looked 10, the cutest little chap you could ever encounter. But as dusk fell it’s like the dark gets them. In the day he was a normal, gorgeous, fun-loving boy – then at night it all changed. He was glue-sniffing, stealing, his eyes hardened over. When it gets dark, the older lads take over and it gets very scary. He went into survival mode.

“Most of them have rotten teeth, and loads have respiratory problems, skin diseases and eye infections because of Manila’s huge pollution problem. They all swim in the river, which has pipes every few hundred feet dumping in raw sewage.

“The kids can’t wash regularly, so one day we followed them to a fire station where they were hoping to wash, but the firemen had locked the hydrants because water is so expensive. I watched as seven of them all tried to clean themselves in a filthy puddle behind a parked car. I sort of lost the plot at that point,” she says quietly.

Deeley has never been called on to make a trip like this for Unicef before; only the biggest stars, such as Angelina Jolie, get to do it. But these days Deeley, who lives in Los Angeles, is a roving reporter for Jay Leno on the Tonight Show and does segments for Good Morning America. Her life is a whirl of massive ratings, thousand-seat studios, personal assistants and a giddying degree of public attention.

Deeley is part of a wider invasion of British talent on US screens. American Idol with Simon Cowell is the country’s top-rated show, while Hugh Laurie is fast becoming their most beloved actor as a grumpy yet brilliant doctor in House.

What’s their secret? “Who knows?” jokes Deeley. “But we meet every week at midnight for a clandestine dinner at Simon Cowell’s house – Nigel Lythgoe, Simon Cowell, Simon Fuller and me plotting our invasion like generals, placing our tanks on a map of Hollywood.” She laughs. “A lot of it is down to the shows. We’ve always been really good at light entertainment in Britain.

“And it means I’m able to do project like this,” she says of her Unicef trip. “You see, the real difference for the kids in Manila is education. Unicef funds street educators, former street children who travel around with a mobile school in a van, who work with the kids teaching them everything from the alphabet to real basics like washing your hands after you go to the toilet.

“I’ve always known there was life outside the celebrity bubble – I just hope that seeing this everyone else does too.”

Please donate to Unicef by calling 0844 822 8888 or visiting www.unicef.org.uk/socceraid

Soccer Aid is on ITV1 tonight at 6pm

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