TRAINER Brian Kan Ping-chee is determined to prove his innocence after the Royal Hongkong Jockey Club yesterday revealed that his horse, Top News, tested positive for the stimulant caffeine following a Happy Valley race on April 21. Kan, the man they still call ''The Champ'' due to his dominance of the sport in the late 1980s, is adamant that he had no contact with Top News for a day and a half prior to the race. ''I'm not worried as I'm innocent,'' Kan said before a meeting with his stable staff yesterday afternoon. ''I just want to know what happened, as for 35 hours I did not see this horse. ''Last week I went to Tuesday morning stables as normal and then to the track to watch my horses work. After that I did not touch this horse at all. ''That afternoon I had business to attend to and did not go to my stables. Instead, I telephoned my head lad and assistant trainer and they said there were no problems. ''On Wednesday I went straight to trackwork and when I came back to the yard Top News had already left for Happy Valley. I did not see him again until about 7.30 pm, before the races.'' Caffeine is a quick-acting stimulant on a horse's central nervous system and therefore a powerful performance enhancer. Because it has such a potentially dramatic effect the Jockey Club allows no trace at all. But if caffeine is administered too close to a race it can impair a horse's performance. Top News, starting at the relatively unfancied odds of 9.4-1, ran home seventh of eight runners. One theory is that there was a lapse in security at Happy Valley's Shan Kwong Road stables or on the journey to there. Top News passed his pre-race screening for drugs, which took place at Sha Tin in the early hours of race day. It is understood that the caffeine revealed after Top News had run unplaced could not have shown up by laboratory error. Nor is it believed that such a positive result could have been due to contaminated foodstuffs. A stewards' inquiry headed by Mr Alan Li faces the task of identifying the source. Jockey Club officials repeated that while every effort would be made to hold the inquiry as soon as possible, it was likely to be weeks rather than days before all investigations were completed. Kan and the horse's owners, the Chinese Press Association, are likely to want a second sample, taken at the same time as the first, tested independently. Anyone found responsible for doping a horse is liable to disqualification or a heavy fine. But under Jockey Club rules, the trainer can be held culpable even if there is no direct evidence, on the basis that he must take ultimate responsibility for security and welfare of his horses.