A pair of cops-turned-robbers yesterday lost their bid to clear their names and get out of jail. Detective constables Ng Chi-wai and Woo Lai-wing, both 40, are serving lengthy prison terms for plotting to rob a fruit shop with knives and a fake gun. The two men yesterday told the Court of Appeal the trial judge's instructions had biased the jury against them. But Mr Justice Barry Mortimer and Mr Justice Simon Mayo rejected the appeal, upholding the convictions and sentences. In the High Court last May, Mrs Justice Verina Bokhary jailed Ng for 12 years and Woo for nine years. The court heard an undercover agent, the Organised Crime and Triad Bureau's Constable Yiu Sung-chi, exposed the racket after a tip-off. On September 29, 1995, he approached Ng at a Mongkok restaurant and told him he wanted to join him. Later that day, the plan was hatched in Ng's office in the Shamshuipo police station. Ng showed the agent a knife, and rolls of adhesive tape and strips of wire for binding, gagging and blindfolding victims. That night the officers went to a Causeway Bay fruit shop. They took an imitation pistol, knives, gloves and wire to tie up their victims. But they abandoned the plan because Ng said too many police were around. Ng and Woo pleaded not guilty to conspiracy to rob. A third officer, Ng Yuk, 41, was acquitted of the same charge.