A DRIVER tried to extort $500,000 from the makers of the drink Yakult by threatening to poison the product, the High Court heard yesterday. Chen Chun-man, 31, an employee at an old people's home, denied he tried to blackmail the company and has gone on trial before Mr Justice Leong and a jury. It is alleged that Chen committed the offence in September 1991, when he made several telephone calls to the Yakult company in Wai Yip Street, Kwun Tong, making unwarranted demands with menaces for $500,000 from Mr Lam Kei-biu. The court was told that Chen, who is being defended by Mr Stephen Franklin, made a series of telephone calls which police traced to restaurants in Tsing Yi. Acting Crown Prosecutor Mr Steven Wong said the calls were made between September 3 and 13. On the morning of September 3, Mr Lam was told by his operator that a caller wanted to lodge a complaint. The caller demanded $500,000 and said he would ''add something'' to the drink, Yakult, if he was not paid. The police were notified. Several more phone calls were made. Two police officers, posing as directors of the company, negotiated with the extortionist. One of the officers was told that if the $500,000 was not paid, the caller would advertise in newspapers that the Yakult drinks had been poisoned, counsel said. That call was traced to a restaurant on Tsing Yi Island and on the morning of September 13, police staked it out. When the suspect emerged from the restaurant, police followed him to an old people's home and when he came out of the building they arrested him. Later, the Yakult company phone number was found written on a piece of paper in the defendant's flat. The hearing continues.