AT the beginning of the Arrow War, 1856-1860, between Britain and China, there was a period of relative of calm, a phoney war, when neither side had the strength to attack the other. The war was unpopular in England, and peace would probably have broken out had it not been for Commissioner Yeh's guerilla tactics. On January 15, 1857, Yeh attempted to poison the European population of Hong Kong by lacing the bread supply with arsenic. The theory was that only Europeans ate bread. The plot went horribly wrong: ''We believe it is the custom of the Parsees and other natives of India to eat an early first breakfast,'' wrote the Hong Kong Register. The result was that there were a lot of sick Indians that morning and most of the Europeans escaped poisoning. Nobody seems to have tipped off the unpopular governor, Sir John Bowring. ''Not one of my family escaped,'' he wrote ''and I had several guests all of whom ate the poisoned bread. Lady Bowring suffered much, some of the arsenic having got into her lungs.'' The prime suspect was the owner of the Esing Bakery, Cheong Alum. He had left Hong Kong with his family for Macau on the steamer Shamrock that morning. The Captain, Mr Antonio, detained Alum after the Shamrock's crew went down with arsenic poisoning. The European population howled for his blood; but the Governor stood firm. Alum was given a fair trial. Most of the jury had been poisoned; but this did not seem to prejudice the outcome. They pronounced Alum ''not guilty'' on the grounds that there was insufficient evidence to convict him. The result was hailed as a triumph for British justice. Shortly afterwards, entrepreneur George Duddell opened a ''poison proof'' bakery - which was promptly burnt down by Yeh's urban guerillas.