POLICE have pounced on a Wan Chai playground and arrested a heroin dealer who had earlier offered the drug to a Sunday Morning Post reporter posing as an addict. Our investigation into how easy it was to buy heroin on the streets of Hongkong was sparked by the news that anti-drug campaigner Frank White's 16-year-old son Daniel was one of three students expelled from Island School for snorting the dangerous drug. We joined officers at a stakeout of Southorn Playground on Friday night, three days after our reporter had been offered heroin within half an hour of arriving. Mr White had targeted the spot as a notorious area for drug dealers and one his son was familiar with. An undercover police officer dressed in jeans, a sweatshirt and baseball cap posed as a buyer, and police in radio contact and armed with binoculars tracked the movement of suspected drug dealers from vantage points around the stadium. Several deals were witnessed by police and, by coincidence, the undercover agent made his ''controlled buy'' with the dealer who had offered heroin to our reporter three days earlier. Officers moved in to arrest the suspect. A search produced the marked money handed over by the undercover officer, while the sealed heroin-filled straw was taken as evidence and was sent for analysis. The handcuffed dealer was driven to Wan Chai police station and, if found guilty, could face between two and five years' jail. He was later released on $1,500 cash bail, to report to Wan Chai Police Station on August 10. Wan Chai police have made 64 drug-related arrests in the past nine months, 43 for drug trafficking. They have seized 1,606 grams of number four grade heroin - usually about 40 per cent pure and cut with caffeine. Latest statistics show a growing percentage of Hongkong drug users under 21 are using heroin, with a rise from 43 per cent to 62 per cent in the past three years. Buying heroin in Hongkong is frighteningly simple. The Sunday Morning Post went to Southorn Playground, a few minutes from Wan Chai's Gloucester Road police station, a shopping mall for drug users. Our reporter found out how easy it was to ''score'' heroin. The stands were lined with people - old men, young couples, the odd gweilo. On a floodlit pitch a football game was being played and on the far side of the ground, young people crowded around basketball hoops. All seemed normal. But scrape the surface and it is not hard to find a seedy underworld where killer drugs such as heroin are openly sold to anyone with cash to spare and an addiction to feed. Most deals appeared to be struck at the Johnson Road end of the playground, a tree-lined avenue dotted with old men playing chequers. Within minutes a buyer was spotted. A young well-dressed Chinese woman walked along the avenue slowly, obviously looking for someone or something. She reached the end and stood against a railing. She glanced around, and approached a thin scruffily-dressed old man - a dealer. He immediately took her away from the pathway towards an exit, and huddled together, his drugs and her cash changed hands. Later, our reporter approached the same man, asked for heroin, and was escorted away from the crowds to wait in a quiet corner next to the stands. He walked quickly to one of the tunnels under the stadium, but returned empty-handed, and approached another man, who slipped him the drugs. Then he came back to our reporter, and handed over a two-centimetre-long sealed heroin-filled straw. He said it was $150, and later dropped the price to $100. At this point, the reporter turned down the deal and walked away.