Olympic medallist Phillips Idowu told today how he was forced to jump over the fence to get into an athletics track as a child because he could not afford the entrance fee.

Triple jumper Idowu, 29, from Hackney, warned that poor children with top sporting potential may never win medals for Britain because they cannot afford to train.

He used to dodge the £2 admission charge at Mile End stadium two or three times a week after school for several years, before he became good enough to get financial support.

His family could not pay the £2 ticket on top of his bus fare each session.

Last month in Beijing he held up a silver medal in front of cheering fans.

Idowu said it was "outrageous" that anyone under 18 had to pay to train at proper facilities.

Backing the Evening Standard campaign, he said: "It seems a small amount, but paying that and travel three times a week when you're poor is a huge barrier and puts kids off. You only get funding once you're recognised nationally as good, so the first few years of proving that [you are good] are a struggle if you aren't well off. You need to use proper tracks to succeed. I can understand why adults have to pay to use them, but kids? It's ridiculous, outrageous."

He said wider access to grass-root initiatives should be a legacy of the 2012 Games because it could tackle London's gang-crime epidemic. "Give a kid a chance to run or take up some other sport properly and that's a focus for their aggression. They start believing in themselves and see a life that's not hanging around on the streets.

"I was never drawn into that stuff as I always knew I wanted to be a top athlete. I have no idea how I kept at it. It was really tough but once you start there's a drive to win and my PE teachers at school were really encouraging."

Natasha Danvers, who won bronze in the 400m hurdles in Beijing, told how when she was a child she had to train in running shoes that had holes in the toes.

The mother of one, 30, originally from Sydenham, said. "My mum was a single parent who already had more than one job. I had to survive on hand-me-down kit.

"I was lucky I lived within walking distance of Crystal Palace stadium and didn't have to pay a bus fare."

She said hosting the Olympics was a chance to improve opportunities for disadvantaged children that should not be missed: "Everyone who has potential should be able to realise it and go to training after school without worrying about the cost.

"We all want medals for Britain in 2012, but what's the point of holding the Olympics if it all falls apart and the money drains away once the TV cameras have gone? It would be awful if someone who could have been me - or better - turns their back on sport because they can't afford it."

She added: "The Olympics and sport in general is about community spirit, and that can change attitudes and lives. It's a way of boosting self-esteem and getting kids off the streets. We want that to last way after 2012." Idowu said sports stars had a responsibility to inspire young people and mentoring schemes should be encouraged. "Seeing top high jumper Dalton Grant train at Mile End one day after school really pushed me on," he said. "I reminded him years later that I'd got him to autograph my homework diary."

He added: "The welcome back I've had from Beijing has been incredible. It will be an unbelievable, life-changing experience for British sportsmen and women who win in London. I'm determined to take the gold in 2012 and push on for another four years, so who knows who I can inspire in that time."