A LACK of witnesses has slowed a police inquiry into the alleged beating of two customs officers by more than 10 policemen in a Hunghom restaurant. Police Commissioner Mr Li Kwan-ha ordered the Complaints Against the Police Office (CAPO) to mount a quick investigation into the case and submit results to the police complaints committee. A senior staff officer of CAPO, Senior Superintendent Ross Williams, said yesterday that investigators had made fruitless trips to the restaurant at the junction of Gillies Road South and Baker Street. ''Our officers have gone to the scene several times, but the response was not very good,'' he said. ''We are still looking for possible witnesses.'' Customs officer Mr Yeung Hak-kwong gave a statement yesterday while his colleague, Mr Tang Kwok-keung, will meet CAPO today. Superintendent Williams said accused officers from the Kowloon West emergency unit and the Hunghom police station would be interviewed later. The customs officers claimed they had been kicked and prodded with batons shortly after an attempt to intervene in an unrelated police arrest which they said involved excessive force. Mr Yeung and Mr Tang, both 28, are each on $5,000 bail for obstructing police and resisting arrest. Mr Yeung, who was admitted to Prince of Wales Hospital for a night after the incident, will be admitted again tomorrow for treatment for a lung injury. The Junior Police Officers' Association said yesterday it was dissatisfied with Mr Li's order for a full investigation into the case.