Tian Liang knows what it is like to be at the heart of China's secretive state-run sports sector. Plucked from the long-jump pit on the school playing fields of Chongqing at the age of 7 and sent to the swimming pool, he was carefully nurtured to become one of the country's most successful divers. During a 20-year career he won three world titles, 15 World Cups, two Olympic gold medals and a bronze.

The 28-year-old also knows what it is like to be cast out of the system. Despite his two-medal haul in Athens in 2004, he was kicked off the national team in 2005 for endorsing everything from electric bicycles to seafood snacks. His coaches, who demoted him to a provincial team despite his continued superiority, said that he had been “violating team regulations concerning commercial activities ... and producing a negative influence on the preparation for the 2008 Olympics”.

As a result he will not be fulfilling the dream of every Chinese Olympian this August and competing in front of his home crowd. Instead, Tian is likely to be in front of a microphone for CCTV, the state-owned broadcaster, after officially retiring last March.

It may be the threat of losing the commentary work that makes him so loath to criticise the system that took his childhood, celebrated him as a national hero and then spat him out as soon as he became bigger than the sacred collective.

In London this week for the Mayor's Chinese New Year celebrations, Tian denied that his two-year exile from the establishment was a factor in his decision to quit. “They did not forbid it [commercial work] and there are a lot of athletes competing in Beijing who are doing it. My retirement had nothing to do with it. It was time for others to get the medals,” he said.

His party-line stance ignores the point that, while endorsements are not officially forbidden - indeed, they are encouraged on the understanding that the state reaps half the reward - Chinese athletes going too far in the pursuit of individual gain are soon out in the cold.

Guo Jingjing, a fellow Olympic gold medal-winner and an old flame, was also ostracised but saved her place in the team by publicly apologising. Similarly, Wang Zhizhi, the basketball player who appeared in the NBA, was welcomed back after four years as he acknowledged his mistakes.

Tian, however, refused to feign contrition. He continued to pursue “selfish” interests, landing a film role and marrying Ye Yiqian, a finalist in the Chinese equivalent of The X Factor.

In a rare off-message moment, he defended his pursuit of fame and fortune. “These [commercial] activities did not affect my training and my life is enriched because of them,” he said, before emphasising that he quit because he was past it. “I was considered an old athlete. When I got the gold medal in 2004, I thought about it [competing in Beijing], but there was a gap of four years and the peak of competition does not last that long.”

Instead he said that he will be satisfied watching from poolside as the China team aim to win all eight diving gold medals this summer. In Athens they won six and at the World Championships last year they took all but one of the ten titles. The divers are under pressure to achieve a perfect eight, the luckiest number in China.

“Being good is different from being perfect,” Tian said. “People are a bit nervous because this is the first time Beijing has hosted the Games and they want to perform well.”

In the glare of international attention, China's world dominance in diving, which emerged in the mid-1980s, could crack along with the mental state of their athletes - the diving team are being forced to undergo weekly psychological assessments to counter stress. But, even under close scrutiny, the training methods - said to be state secrets - are unlikely to be demystified for foreigners.

Tian, who trained for six hours a day and started competing at the age of 8, offers no clues as to how the totalitarian apparatus works. “There is no secret. What we did was known by everyone,” he said. “In the team we were friends, but if you let someone get the gold medal, you didn't get it.”

At least one thing is certain: he will not be getting one in Beijing.

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