LONDON - "Smell that," says Tim Smit, clutching a handful of earth scooped up from the ground at London's Olympic Park.

Smit is one of the sustainability ambassadors who have been involved in transforming the East London site from an under-developed, contaminated and polluted expanse of brownfield to a green wonderland.

The heap of soil in his hand unsurprisingly smells of earth and is proof, he says, that there is no place, no matter how deprived or run-down, that cannot be redeemed.

"Not one grain of this earth is original," Smit, who was co-founder of the Eden Project in Cornwall, said. "It has been made in the biggest soil manufacturing contract in history.

"What you see is a real symbol of hope for some of the crappest places in the world."

As he says this we are standing by the River Lea, that cuts through the North Park of the Olympic grounds.

Surrounded by wild meadows, teeming with purple, white and yellow flowers and bordered by a reed beds, it stands in stark contrast to its former condition.

The waterway, used for industry for over a century, used to be vertical-sided and choked with rubbish, littered with shopping trolleys and old cars that made it unnavigable and unpleasant.

The river is one part of an astonishing turnaround that has seen a patch of polluted wasteland transformed into an impressive nature reserve that surrounds the venues that will play host to the world's athletes in a few days time.

The Olympic Park itself is about 50 hectares. That makes it the largest new park in Britain for over a century, according to Phil Askew, who is head of parklands and gardens on site.

"In this sense we are adding to the great Victorian tradition of urban parks," he said on a tour of the vast Olympic grounds.

The site is divided into the North and the South parks.

The North is verdant with extensive meadows that are fundamentally about bio-diversity and beauty.

In the South, they have gone for masses of colour in four separate gardens, thematically spanning Europe, Asia, the southern hemisphere and North America.

Down south is much more horticultural and decorative but the underlying idea is the same. It plays host to an array of butterflies and insects that according to Askew show that "you can have your cake and eat it...it looks fantastic but it does a great job ecologically."

What was often referred to as a "toxic waste dump" now houses 200-300 hundred plant species, native and non-native.

"It has been extraordinary to see this complete change in an area that was rank with rough vegetation, dereliction, polluted ground only a few years ago," Askew added.

Des Smith, one of the head gardeners, responsible for bedding nearly 70,000 plants, describes the scene as a "massage on the eyeballs" and "an assault on the senses".

The site is quite a contrast to its equivalent in Beijing four years ago. The Chinese capital, while feted for the design of some of the venues, offered an urban environment and was a mass of concrete, with few green spaces.

Those responsible for regeneration in London hope their efforts will provide the template for Games to come.

"This is going to be the day the Olympics changed," said sustainability ambassador Deborah Meaden, a business woman and television personality in Britain.

"It is really groundbreaking stuff. The heartbreaking thing is that you can't see it," she said referring to how the landscape has changed.

Smit added: "(Unlike) other Olympic sites, it doesn't scream about fascistic powers of the state.

"Everything is intimate. There are intimate spaces where people can feel human and that is deliberate. You can imagine kissing somebody here."