China's UK embassy has rejected claims by a former employee of Britain's Consulate in Hong Kong that he was tortured by the Chinese police.

In a statement, the embassy said that Simon Cheng had been legally detained and his rights had been observed.

Cheng, who said he had been gathering information on the Hong Kong protests as part of his job, was held after visiting the mainland in August. He says that he was accused of soliciting a prostitute, but refused in a BBC interview to address the issue, claiming that would play into the Chinese authorities' hands. 

While in detention, he says that he was beaten and subjected to other ill-treatment while being questioned about the activists behind the protests against Chinese influence and policies.

In a tweet the Chinese Embassy said: "Simon Cheng was placed under a 15-day administrative detention by police in Shenzhen last August for violating the Public Security Administration Punishments Law of P. R. China. He confessed all his offences. All his lawful rights & interests were guaranteed in accordance with law."

Cheng, a Hong Kong resident, made his claims on a Facebook post and in an interview with the BBC. 

He said he was forced to make a written confession and told that if he spoke about his experiences he would be spirited out of Hong Kong back to mainland.

"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.

Britain's Foreign Secretary Dominic Raab said Cheng's account was credible and that the treatment amounted to torture. He raised the issue directly with China's ambassador Liu Xiaoming. 

The statement from China's embassy said that during the meeting, in addition to denying Cheng's accusations, Liu Xiaoming criticized Britain's involvement in condoning the violent acts of protesters in Hong Kong who have attacked police with petrol bombs, rocks and arrows. He urged the government in London to stop interfering in China's internal affairs. 

Hong Kong, which the UK handed back to China in 1997, enjoys relative autonomy under "One Country, Two Systems" but has been wracked by protests against Beijing's influence since June. 

Questioned about Cheng's case at a press conference, Hong Kong's justice secretary Teresa Cheng urged him to report the incident to the correct authorities and said she would look into the matter if it were raised with her.

Simon Cheng, who said he supported the Hong Kong pro-democracy movement, say he would not seek judicial redress as he had no faith in the Chinese legal system. The BBC reported that he is seeking asylum.