A SENIOR Immigration Department official yesterday refused to reveal the Government's priorities covering the removal of Vietnamese boat people from Hong Kong. Choy Ping-tai, assistant director of the Vietnamese Refugees Branch, told the High Court that the system meant some migrants were detained for up to two years, while others repatriated within a few months. But when asked to reveal how the system worked Mr Choy said: 'I do not want to answer this particular question because the information may jeopardise operations in the future.' Mr Justice Keith said: 'So you do have a system of priorities, but you don't wish to reveal how the priority system works, because you feel that might jeopardise future operations.' Mr Choy was called as a witness in a landmark habeas corpus action launched by five asylum-seekers. The action could land the Government with a large compensation bill for illegal imprisonment. Peter Graham, representing the asylum-seekers, was given permission by Mr Justice Keith to cross-examine Mr Choy on specific matters dealt with in written statements he made to the court. Mr Graham questioned the civil servant about Tan Le Lam, 43. The court heard that Tan was detained pending removal on May 21 last year, but his personal particulars were not sent to the Vietnamese authorities until December 8 this year. Mr Choy agreed that no one could be removed from Hong Kong under Section 24 of the Immigration Ordinance until details were given to the Vietnamese Government. 'Why was this not done until about 11/2 years after he was first detained pending removal?' Mr Graham asked. He added: 'Is there any reason why the particulars could not have been sent to Vietnam straight away?' Mr Choy said one reason was that the Immigration Department wished to persuade boat people to return to Vietnam voluntarily with dignity and in safety. The Vietnamese Government's lack of resources was another reason for delays, he said. In a written statement made to the court, Mr Choy said under the forced repatriation programme, personal particulars of about 12,000 migrants were sent to Hanoi. More than 5,500 names had been returned with positive identification. Cross-examination of Mr Choy continues today.