Reports of police officers abusing prostitutes almost doubled in the first quarter of this year, a sex workers' rights group says. Zi Teng collected 88 such reports in the first three months of the year, up from 47 in the last quarter of last year - far exceeding the number of complaints by prostitutes about other clients. The reports include 15 cases of police officers receiving sexual services without charge before making an arrest and 31 of officers receiving massages. Police rules state that, under the direction of a senior officer, undercover police can receive masturbation from a prostitute but no sexual services beyond that. 'The reasonable way for the police to do their job is to stop receiving the service once it has clearly begun, but all reported cases showed that they did not reveal their identity until after the entire service had ended,' Zi Teng founder Yim Yue-lin said. The group believes many prostitutes, especially migrant workers, do not report such incidents. A police spokesman said the force did not record how many arrests were made at unlicensed massage parlours. He said undercover policemen worked under a strict set of rules. The officers worked under the direction of deputy regional commanders or senior superintendents, whose job included ensuring limited sexual services were accepted when necessary. Working as a prostitute is not illegal in Hong Kong, but soliciting clients and running a brothel are banned, although so-called one-woman brothels are tolerated. But the law leaves sex workers open to exploitation, prostitutes' rights groups say. With brothels outlawed, women cannot band together for protection. Zi Teng is also concerned about a sharp rise in the number of foot-massage parlours, at which some masseuses illegally offer to masturbate clients. It says there are now 2,000 foot-massage parlours, which do not require a licence - almost twice as many as last year. 'It is really beyond our expectation to see the sharp increase in the number of massage parlours, especially the foot-massage parlours,' the group said. Many of the masseuses were new immigrants from the mainland who took government-run retraining programmes in massage, it said. But while skills and theories about massage were taught in the programme, it did not cover the law about massaging the opposite sex and setting up massage parlours, it said. The law requires massage parlours to apply for a licence only if the operator offers massage services to a client of the opposite sex between shoulder and knee. Only 150 such licences have been issued. But the group believes many masseuses think taking the government course grants them a massage licence.