A WORKING group studying the abolition of the Office of Members of the Executive and Legislative Councils has recommended that its London office be retained for another three years at an estimated cost of $11.5 million. The Legco Working Group on the Winding Up of Omelco has agreed that the office should be renamed the Legco London Office and kept open until March 31, 1996. This is despite the fact that some legislators have cast doubts on the value of keeping the office as it is not cost-effective, given the thin volume of work for its staff. The London office was established for an initial period of three years in April 1990 to help legislators lobby for passports and more directly-elected seats. Its former chief, Mr Alastair Lang, resigned last July because of ill health. His $1.5 million ''golden handshake'' caused a controversy among legislators. At that time, it was widely expected that the office would be closed when the three-year period expired and no effort was made to find a replacement for Mr Lang. Since Mr Lang's resignation, the office has been staffed by a public relations adviser, Mr Ross Clarke, and an office manager. The adviser's annual salaries and allowances are expected to top $836,000 in 1993-1994. It is understood that some officials are also doubtful about maintaining a separate Omelco office in London because much of its work overlaps that done by the Government's London office. One of the key functions of the Omelco office is to lobby British politicians on Hongkong affairs which is also a routine task of the Government's London arm. But working-group members, without offering any concrete plan, believe the functions of the office should be expanded, which might also necessitate the hiring of a senior assistant secretary. However, members were split on whether the Legco office should move to the same premises as the Government's office. About $1.2 million could be saved in office rentals and hiring conference facilities if the two were merged. It takes only about 30 minutes to walk between the two offices, both of which are in Westminster. Meanwhile, the deputy president's working group on the re-organisation of the Legco secretariat has agreed that the secretary general should assume the role of the principal clerk of Legco and be the chief adviser to the president on procedural matters. A new post of deputy secretary-general should be created to provide assistance. At the same time, the press section of the secretariat believed that the ranking of its chief, now a D2, should be downgraded to D1. It said the change was justified by the fact that the role of providing public relations advice and strategy for legislators had gradually been taken over by the personal assistants of the councillors. The post was occupied by Mrs Betty Shum Sheung Yin-yuk until yesterday. Her new job is to be press secretary to the Executive Council.