LONDON - The British Foreign Office has summoned China’s ambassador after a former employee of the British consulate in China alleged he was tortured by Chinese police.

Hong Kong citizen Simon Cheng said he was tortured during a 15-day detention by police in mainland China.

Cheng said Chinese secret police shackled him, beat him and deprived him of sleep while they questioned him on the UK’s role in Hong Kong’s pro-democracy protests.

“I was hung (handcuffed and shackled) on a steep X-Cross doing a spread-eagled pose for hours after hours,” Cheng said in a post on Facebook.

“Sometimes, they ordered me to do the ‘stress tests’, which includes extreme strength exercise such as ‘squat’ and ‘chair pose’ for countless hours. They beat me every time I failed to do so using something like sharpened batons.”

Foreign secretary Dominic Raab summoned the Chinese ambassador to the UK to explain the “disgraceful” treatment Cheng had received.

“Simon Cheng was a valued member of our team. We were shocked and appalled by the mistreatment he suffered while in Chinese detention, which amounts to torture,” Raab said.

“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.

Cheng said he was arrested inside West Kowloon station in Hong Kong in August on his return from a trip to mainland China for a business conference.

Read more: Top MP denies British interference in Hong Kong after Chinese ambassador’s warning.

China has a controversial border post inside the station which was opened following the launch of the Hong Kong-Shenzhen high-speed rail link last year.

Hong Kong’s pro-democracy protesters view the border post as another example of China’s encroachment on Hong Kong’s freedoms.

Cheng was forced to give a written confession for betraying the motherland, a statement of apology and a confession for “soliciting prostitution”. He was instructed to sing the Chinese national anthem and recorded singing.

“I won’t give up the fight for human rights, peace, freedom and democracy for the rest of my life, no matter the danger, discrimination and retaliation I will face, and no matter how my reputation will be stained, and no matter whether my future would be blacklisted, labelled, and ruined,” Cheng said.

China’s UK embassy was contacted for comment.