IT'S time to sell stocks. Broker Mr John Mulcahy is changing jobs. The Peregrine Brokerage regional research director has a record of taking up new positions at times of market carnage. He moved into broking as a vice-president with Citicorp Scrimgeour Vickers in October, 1987, at the time of the crash, and took on his present role on June 1, 1989, just three days before the Tiananmen Square massacre that knocked the local market for six. Mr Mulcahy leaves Peregrine at the end of February and, after a month ''in the freezer'' to protect company confidentiality, becomes managing director of UBS Securities after Easter. ''We may be in for a bit of a crack in the market if my history is any guide,'' he joked yesterday. The market, of course, recovered from the crashes. Mr Mulcahy's career has also moved ahead rapidly. The former South China Morning Post and Far Eastern Economic Review journalist has helped build Peregrine into one of the most successful investment houses in the region. He started its research department from scratch and believes it is now as good as any in the market. So why leave for UBS, a comparative minnow in the Hongkong market? ''After running a large division in a company, the opportunity to run a small company, but in its entirety, appeals,'' said Mr Mulcahy. ''I am going to try to build another franchise. Hongkong is crowded with brokers, there are over 600 active, but is the world crowded with brokers delivering quality products in this region? ''The franchise in Hongkong really does offer a lot of scope for development and leveraging on the UBS brand name. It is the biggest Swiss bank, with an existing global securities business.'' Mr Mulcahy will be in charge of both research and trading. He will report to UBS's regional headquarters in Singapore. The company is planning to open offices in Thailand and Malaysia.