THE Government is insisting that the legislation intended to crack down on organised and serious crime should include ''one-off'' offences, a provision criticised as open to abuse. The Security Branch told legislators in a paper yesterday that the administration, though facing opposition from legislators and legal practitioners, had no intention of excluding such offences from the definition of ''organised and serious crimes''. It said existing powers were inadequate to investigate and prosecute those responsible for planning and directing one-off organised crimes. If the clause was removed, ''then criminal syndicates will quickly learn to escape the provisions of the ordinance by reassociating themselves after committing one crime, thereby making detection and investigation impossible''. Legislators had called for the clause to be deleted since one-off offences, even if they were also substantially organised, could be investigated with existing powers. The Bar Association backed the argument, saying that law-enforcement bodies would find it easy to invoke that clause. For example, two schoolgirls who stole a bar of chocolate from a supermarket after substantial planning and organisation - for instance, staying up at night to plan the theft and making escape plans - would be covered by the clause, it said. The association called for a tighter definition of ''substantial planning and organisation''. The bill would give wide-ranging powers to law enforcement bodies to compel witnesses, victims or accomplices of criminals to answer questions and provide information and materials. The Government said the powers were necessary because it was no use producing a search warrant unless the location of information was known, which was a very time-consuming process. A request by legislators to add a provision to the bill forcing the Government to submit to them a report reviewing the effectiveness of the bill, was also rejected by the branch.