China can be prevented from repeating all five titles in the world championships at Wembley arena next week, according to Tine Baun, the former world number one from Denmark. China's brilliantly taken clean-sweep at the world championships in Paris a year ago has brought speculation that it will become the first badminton nation ever successfully to defend all the titles. And because these world championships are at the same Wembley venue as the London 2012 Games, they will be a pointer to China's chances of also becoming the first badminton nation to win all five Olympic titles. Four of the five top seeding spots next week are filled by Chinese players, but this does not apparently discourage Baun. "They are very good but they also have their ups and downs. They have shown lately they can be beatable," she said, hinting at her victory over Wang Shixian, the world number one, in Singapore in June. "I know China are very good, in all categories. They are really well prepared, and every time they play a championship they are delivering every time. "But I am not worried about it. I think some other countries are making good improvements. And some events are open." Much may depend on Lin Dan, regarded by many as the greatest player ever, because the men's singles is the only event in which China does not have the top seed next week. Instead that is Lee Chong Wei, the dazzlingly nimble Malaysian who beat a rather muted Lin in the All-England Open final in Birmingham in March. However the second-seeded Lin is the only player ever to have won three world men's singles titles, and with the possibility of retirement after London 2012, he may rediscover the appetite for a fourth. He is still only 27. Lin is seeded for a semi-final with Peter Gade, the former world number one from Denmark, and Lee with Taufik Hidyat, the former world and Olympic champion from Indonesia. The defending champion, Chen Jin, also Chinese, may have a quarter-final with Hidayat. "Maybe the men's singles is open," Baun commented. "China's ladies doubles is at a very high level, but has not delivered like before. And I think the men's doubles is very open. And the mixed doubles. "And perhaps we can hope for an opening in the women's singles," Baun added with a touch of humorous self-interest, before repeating: "but China is really good at delivering." Indeed China is a stronger favourite in the women's singles than any other event, even though Baun twice denied strong Chinese challenges from taking the All-England Open title in the past four years. "All four (top Chinese) can win the women's singles," added Baun. "I think maybe Wang Xin and Wang Shixian have a very good chance. But I think Wang Yihuan wants to deliver a medal as well." Baun spoke of irregularities involving Chinese players during the All-England Open, alleging unsatisfactory outcomes in matches between compatriots and also complaining that Wang Yihan had not made a mandatory appearance after withdrawing from the tournament. These and other controversies have caused the formation of a special panel by the Badminton World Federation, which now looks into alleged breaches of the player commitment rules. It concluded that Wang Yihan had been unable to travel to Birmingham due to an injury. The BWF waived a fine upon the former All-England champion, who is now reportedly fit again and is seeded to reach the final at Wembley. Baun is in the other half, which is topped by Wang Shixian, but the Dane may need to survive a quarter-final with Jiang Yanjiao, the fourth seed. "The BWF has been looking into player withdrawals to prevent further speculation in this area," commented the BWF's chief operating officer Thomas Lund. "We expect that there will be an outcome of this work from our executive board meeting during the world championships."