THE 74-year-old former chairman of the Union Bank, Oen Yin-choy, yesterday sought a permanent stay of commercial crime charges on the grounds he was suffering from dementia and was unable to instruct his lawyers. After hearing evidence from the world's leading neurologist, Lord Walton, that Oen's condition continued to deteriorate, the Crown decided not to pursue the prosecution and entered a nolle prosequi in the High Court yesterday afternoon. Lord Walton testified that Oen was suffering from an organic brain disease, which was probably caused by Alzheimer's disease. His mental process was slow and his intellectual capacity was substantially impaired; there was no doubt he was suffering from dementia. Oen faced four counts of false accounting, in which he was alleged to have falsified documents to show that loans amounting to $210 million were made to four companies in 1984, and one count of making a false statement in the bank's 1985 annual report. He left Hongkong in 1985 and the Government took over the bank. Oen was extradited from the US in 1989 after a 21/2-year battle. Alan Hoo QC, for Oen, told Deputy Judge Daniell that his client had suffered from heart disease since 1982, and had had a triple coronary bypass. He also has a liver condition, suffers from hepatitis B and C and is believed to have Alzheimer's disease. Although on bail of $5 million, Oen has been in hospital most of the time since returning to Hongkong. His trial was originally fixed for August 1991, but his lawyers were unable to get instructions from him. A psychiatrist and a neurologist both concluded Oen was suffering from dementia. Lord Walton agreed after further examinations. The trial was postponed and the Crown's doctors examined Oen. Mr Hoo said both sides agreed that Oen was suffering from dementia and was incapable of comprehending the evidence and of giving meaningful instructions to his lawyers for the preparation of his defence. Last July, Oen's lawyers wrote to the Attorney-General inviting him to offer a nolle prosequi but, in April, the Attorney-General decided not to do that and said Oen should apply for a stay. Mr Hoo said defendants were guaranteed the right to a fair trial under Article 10 of the Bill of Rights. Because Oen suffered from organic irreversible dementia, giving rise to severe cognitive impairment and was unable to instruct his lawyers to establish a proper defence, he would be unable to have a fair trial, Mr Hoo said. After lunch, deputy principle Crown counsel, Graham Harris asked for an adjournment to consult with the Attorney General. He later told the court that having heard Lord Walton's evidence, particularly his recent examination the previous night of Oen which shows a further deterioration in his condition and discussed it with the Crown's expert who agreed with Lord Walton, the Attorney General now believed the best interests of justice would be served by entering a nolle prosequi . Deputy Judge Daniell said he thought it a sensible decision.