A police officer claims the Hong Kong force has become a 'political tool', after a demonstrator was arrested for spraying a central government liaison office security guard with champagne. Some senior officers were shocked and shamed by the detention of Ip Ho-yee, the officer, who did want to be named, said. Ip, 22, was arrested - but later released - after a celebration held outside the office on Sunday to mark the award of the Nobel Peace Prize to mainland dissident Liu Xiaobo . The officer said: 'This case makes the force look like a political tool, a low-class one.' Law Yuk-kai, the director of Hong Kong Human Rights Monitor, said: 'This arrest was a common insult to all Hong Kong people, which did not make sense at all. [The police] lost their professional judgment and became political clowns in this case.' Veteran democrat Szeto Wah said Ip's arrest was a joke. 'This was intentionally carried out by the Hong Kong government. The government has allied with the liaison office to suppress the democratic movement in Hong Kong in the past year,' Szeto said At Sunday's celebration, activists ate Norwegian salmon to show their support for the Oslo-based Nobel committee - which has been heavily criticised by Beijing over the award - and opened bottles of champagne. Ip said that she had not meant to spray champagne on the guard. 'Three bottles of champagne were brought. I helped to open the second bottle, which was quite difficult,' she said. She said she saw the guard behind the liaison office gate was unhappy that he was wet. 'But I had no intention to target him; all the people there got wet as champagne splashed,' she said. Ip said that as she was leaving half an hour later, a police community relations officer asked her to help with an investigation. 'The officer said police had received a complaint about the champagne splash. After I refused to assist the investigation, there was a silence of several minutes before the officer formally told me I was being arrested for common assault,' she said. She was later granted bail in the sum of HK$500 and told to report to police next month. Eric Cheung Tat-ming, associate professor of law at the University of Hong Kong, said police should do more investigating and collect more evidence before exercising their power of arrest. Hong Kong police did not respond to the criticisms.