China warned the UK not to meddle in its affairs over Hong Kong on Wednesday after the arrest of a British Consulate official worsened already strained ties between Beijing and London. Simon Cheng, 28, a trade and investment officer at the Hong Kong consulate’s Scottish Development International section, went missing on August 8 on the way back from a business event in the Chinese city of Shenzhen. Britain has said it is “extremely” concerned. News of his disappearance became public on Tuesday, prompting China on Wednesday to confirm that it was holding him on allegations of violating local law, without revealing any further details. Geng Shuang, the Chinese foreign ministry spokesman, said the case was linked to China’s Public Security Administration Punishment Law, a statute pertaining to minor violations. Individuals can be held under administrative detention for as long as 15 days, which would be roughly until Friday. Mr Geng warned the UK to back away from the affairs of its former colony. “The British side has made a lot of erroneous remarks on Hong Kong,” Mr Geng said, urging London “to stop pointing fingers and making accusations.” “He is not a British citizen. He is a Chinese person, so this is entirely a matter of China’s internal affairs,” Mr Geng said of Mr Cheng. “As for Britain’s comments, we’ve made stern representations to Britain for the series of comments and actions they’ve made on Hong Kong,” he said. He also called on Britain to stop interfering in China’s internal business. “Britain has made a series of wrong statements on Hong Kong. We again urge them to stop gesticulating and to stop fanning the flames,” Mr Geng said. Activists gather outside the British Consulate-General building in Hong Kong Credit: ANTHONY WALLACE/AFP/Getty Images In a statement issued on Facebook, Mr Cheng’s family said: “We feel very helpless, and are worried sick about Simon. We hope that Simon can return to Hong Kong as soon as possible.” Friends of Mr Cheng, staged a rally outside the British Consulate in central Hong Kong on Wednesday urging Boris Johnson, the Prime Minister and Nicola Sturgeon, Scotland’s First Minister “save” the young man from a Chinese jail. “Save Simon Now! Delay No More!” they chanted. Max Chung, the rally organiser, who knew Mr Cheng from his student days at the London School of Economics, accused the UK of “failing to show due diligence” towards him. “Mr Boris Johnson, the prime minister, it’s now or never!” he said. “We appeal to Boris Johnson and Nicola Sturgeon, we urge you to save Simon. Make this your number one priority now.” Michael Mo, a fellow protester, added: “England expects every man to do his duty and we expect every British politician to honour their word.” The group was briefly admitted indoors to present a petition calling for the UK to express “specific measures” to protect British Nationals in Hong Kong and to issue a travel warning that British and foreign nationals in Hong Kong could be subjected to “enforced disappearance.” Simon Cheng, a staff member of the British Consulate in Hong Kong, was initially reported missing Emerging from the building, Mr Chung said senior officials had assured him that they were working “full throttle” to secure Mr Cheng’s freedom. However, protesters said that Mr Cheng’s predicament confirmed their worst fears about arbitrary detention by China. The Hong Kong protest movement, now in its eleventh week, began over opposition to a planned extradition law that would allow suspects to be sent to trial for the first time in China’s opaque justice system. “Simon’s case is “white terror” to everyone in Hong Kong. Because even if you haven’t voiced out your political views, you may still be considered a target, and can be arrested for no reason,” said Duff Li, a protester in his twenties. Mr Cheng’s disappearance has also revived fears about the safety of diplomatic personnel in China. The diplomatic and expat community has already been put on edge by the December detention of Michael Kovrig, a Hong Kong-based security analyst on leave from Canada’s foreign service, and by the arrest of Michael Spavor, an entrepreneur, who worked between China and North Korea. China | Read more from The Telegraph Meanwhile, Hong Kong maintained its week long uneasy calm spell on Wednesday night when thousands of protesters gathered at the Yuen Long metro station in the New Territories district on the outskirts of the city to mark one month since a vicious assault on dozens of commuters by triad gangs. Public anger remains high over the incident, in which at least 45 people were attacked by hundreds of alleged gang members wearing white shirts and wielding sticks. The police were accused of responding too late and of being slow to arrest the perpetrators. Protesters crowding the station initially stood in silence, holding one hand over their right eye to symbolise a young female medic who was hit in the face by a police bean bag shot during a demonstration and badly injured But there were tense scenes outside the station as locals hurled angry insults at riot police. “Triad cops! Why didn’t you save us last month? Why are you coming now when nothing is happening?” shouted bystanders. Violence was close to flaring up when protesters pushed police back from the station entrance with fire extinguishers and closed the gates, briefly locking themselves inside. But while the elite Raptors squad lurked on standby, armed with bean bag guns and tear gas, not a shot was fired, and both sides retreated to brace for another weekend of protests as the pro-democracy movement heads into its 12th week.