BEIJING >> A former employee of the British Consulate in Hong Kong says he was detained and tortured by Chinese secret police trying to extract information about massive anti-government protests in the territory.

Simon Cheng said in an online statement and media interviews that he was hooded, beaten, deprived of sleep and chained to an X-shaped frame by plainclothes and uniformed agents as they sought information on activists involved in the protests and the role they believed Britain played in the demonstrations.

British Foreign Secretary Dominic Raab summoned the Chinese ambassador in London to demand Beijing investigate.

“I summoned the Chinese Ambassador to express our outrage at the brutal and disgraceful treatment of Simon in violation of China’s international obligations,” Raab said in a statement. “I have made clear we expect the Chinese authorities to investigate and hold those responsible to account.”

Chinese police in August announced Cheng’s release after 15 days of administrative detention but gave no details of the reasons behind his detention.

China’s foreign ministry responded angrily to the allegations and the summoning of the ambassador at a daily briefing on Wednesday.

Ambassador Liu Xiaoming will “by no means accept the so-called concerns or complaints raised by the British side,” ministry spokesman Geng Shuang said.

“The Chinese ambassador to the U.K. will lodge the complaints with the U.K. to express our strong opposition and indignation to the U.K.’s wrong words and deeds on Hong Kong in these days,” Geng said.

Geng did not address Cheng’s allegations directly, but cited a statement by Shenzhen police from August saying his lawful rights had been protected and that he had “admitted his offense completely,” an apparent reference to a confession of soliciting prostitution that Cheng says was coerced. Cheng has strongly denied the charge.

Police in Shenzhen did not immediately respond to faxed questions about Cheng’s allegations.

Cheng worked for the consulate as a trade and investment officer with a focus on attracting Chinese investment in Scotland. That required him to travel frequently to mainland China and he was detained at the border with Hong Kong after returning from a one-day business trip.

Hong Kong’s nearly six months of pro-democracy protests began in opposition to proposed legislation that would have allowed criminal suspects in the semi-autonomous city to be extradited to face trial in mainland China, where critics say their legal rights would be threatened. While Hong Kong leader Carrie Lam has since withdrawn the bill, demonstrations have continued unabated as strong anti-government sentiment continues.

China says it doesn’t allow suspects to be tortured or make false confessions, although both practices are believed to be common.

In his account on Facebook, Cheng wrote that he had been asked about the supposed British role in the protests, his own involvement in them and mainland Chinese who joined in demonstrations.

China has long accused “anti-China foreign forces” of fomenting the protests, which have grown increasingly violent, without providing direct evidence.

Cheng wrote that while being held he was shuttled between detention and interrogation centers while hooded and handcuffed. In addition to being shackled to the frame, he wrote he was ordered to assume stress positions for “countless hours,” and was beaten with what felt like “sharpened batons” and poked in the knee if he faltered. He was also punished for dozing off during the sessions by being forced to sing the Chinese national anthem, he wrote.

“I was blindfolded and hooded during the whole torture and interrogations, I sweated a lot, and felt exhausted, dizzy and suffocated,” Cheng wrote.

One interrogator speaking Hong Kong’s native Cantonese dialect cursed him, saying, “How dare you work for the British to supervise Chinese,” while another speaking in a northern Mandarin accent told him they were from China’s secret intelligence service and that he had “no human rights in this place,” Cheng wrote.

He said the interrogators expected him to confess that Britain had instigated the protests by donating money and materials, that he personally led that effort and paid the bail of mainland participants. At the detention center, he witnessed police questioning other young inmates who appeared to be Chinese mainland nationals being punished for participation in the protests.

Cheng said he refused but confessed to the minor offense of “soliciting prostitution” in order to avoid harsher treatment and a heavy sentence on national security charges. Some of the officers holding him said they could “abduct” him back to the mainland if he didn’t “behave,” he said.

Cheng no longer works at the consulate and has fled to a third country. Raab, the foreign minister, said the U.K. is working to support Cheng, including a possible move to Britain.