A woman believed to be a reporter for Chinese state media is being held by police after allegedly slapping a delegate in the face during a Hong Kong fringe event at the Conservative party’s annual conference.

Enoch Lieu claimed the woman assaulted him after he asked her to leave the event, entitled The erosion of freedom, the rule of law and autonomy in Hong Kong, at the Birmingham International Convention Centre (ICC), on Sunday.

He said Fiona Bruce MP, who was chairing the event, asked the woman to leave because she shouted at one of the speakers, Benedict Rogers, founder of Hong Kong Watch, accusing him of trying to break up China.

“I approached her, and tried to tell her she had made her point and she was no longer welcome,” Lieu wrote on Twitter. “The reporter continued her shouting and whilst I was trying to escort her out, she accused me of trying to silence her. Then I said: ‘No miss, you have to go.’ All of a sudden, she slapped me in my face.”

“The audience was shocked and some brave men and women came and tried to escort her out. During the struggle, she continued her shouting and refused to leave, then out of the blue again, slapped me again.”

Video footage posted on the Hong Kong Free Press website appeared to show part of the incident. Lieu can be seen telling a visibly angry woman: “You are in the Conservative party conference … please go.”

She responds by appearing to throw a slap, although the video does not show whether it landed.

As others restrain her and try to usher her away, she tells Lieu: “You have no right, you have no democratic [sic] in the UK, I’m a journalist here… I have [a] right to protest.”

Lieu said he had confirmed later that she worked for the Chinese government-owned CCTV.

A spokeswoman for West Midlands police said on Monday: “Police were called to hall 11 at the ICC yesterday at 2.30pm after reports a disturbance had broken out during a talk on Hong Kong. A 48-year-old woman from King’s Cross, London, was arrested on suspicion of common assault. She remains in police custody.”

She said the woman had identified herself as working with a TV company. A spokesman for the Chinese embassy in London said the journalist deserved an apology.

He said: “In a country that boasts freedom of speech, it is puzzling that the Chinese journalist should encounter obstruction in such a way and even assault at the fringe event when she simply raised a question and expressed her opinions. This is completely unacceptable.

“The human rights committee of the UK Conservative party should stop interfering in China’s internal affairs and stop meddling in Hong Kong affairs. The organiser of fringe event should apologise to the Chinese journalist.”

Others speaking at the event were Martin Lee, founder of the Democratic party of Hong Kong, Benny Tai, legal scholar and democracy activist, and Nathan Law, Hong Kong’s youngest elected legislator and a leader in the Umbrella movement.