China had been embroiled in the first doping controversy of the London Games after one of the world's most respected coaches described the swimming prodigy Shiwen's gold medal performance as “unbelievable” and “disturbing”.

Ye Shiwen took seconds off her personal best to break the world record and win a gold medal in the 400m medley on Saturday, swimming faster in the last 50m than the winner of the men's event.

The American John Leonard, Executive Director of the World Swimming Coaches Association, said the 16-year-old's performance was “suspicious” and said it brought back “a lot of awful memories” of the Irish Swimmer Michelle Smith's race in the same event at the Atlanta Olympics in 1996. Smith was banned for four years in 1998 after testing positive for an anabolic steroid.

Leonard had also called for an investigation into the Chinese, saying they could be using genetic manipulation.

However, Shiwen has denied taking drugs to enhance her performance, explaining that there was no problem with doping.

Shiwen said, “There is no problem with doping. The Chinese team has a firm policy so there is no problem with that.”

And BOA Chairman Lord Moynihan said the World Anti-Doping Agency (Wada) was ‘on top of the game.’

“She's been through Wada's program and she's clean. That's the end of the story. Ye Shiwen deserve recognition for her talent,” he told in a press conference.