Supporters of Hong Kong’s pro-democracy protests say they are being intimidated and harassed by pro-Beijing Chinese students and others at their events around the UK, forcing police to step in to separate them from counter-demonstrations.

Below-the-radar tensions have boiled over into incidents that include the arrest of a 19-year-old Chinese student after bottles were thrown at a Sheffield event, while police and university security have intervened in other town centres and campuses.

Hong Kong activists – who complain they are being filmed and photographed – link the counter-demonstrations to UK-based Chinese student organisations supported by the Chinese government.

In London, eggs were thrown at people gathering to attend a concert by Denise Ho – the Hong Kong “Cantopop” star and activist blacklisted in mainland China – where a crowd waved a large Chinese flag and shouted pro-Beijing slogans.

In an apparent nod to a pejorative term used by opponents of Hong Kong activists, some also carried placards with images of cockroaches and the words in Chinese: “It’s everyone’s duty to eradicate pests.”

Inky Wonders (@InkyWonders) Re-edit: Was at @hoccgoomusic's concert on Fri to photo pro-Beijing protesters. They had Chinese flags and signs which say, "It's everyone's duty to eradicate pests."



This flag ended up on the floor and squished by one of their signs.#Photography #Photojournalism #China #爱国 pic.twitter.com/aZTvT0gHkR

Hong Kong students at an event in Birmingham on 12 October said they had been followed and filmed by older Chinese men and grabbed by one who attempted to remove a student’s mask. The next day, the same men turned up at Aston University’s campus at a documentary film screening by Hong Kong students, and were later blocked by security.

The university told the Guardian that its security team had refused re-entry to the event to a small number of individuals whose behaviour had been disruptive. Adding that it was aware of incidents in the city centre, the university said its priority was to ensure the safety of students, while protecting freedom of speech.

One Hong Kong student said: “Although physical assaults are also one of our major concerns, what worries me the most is how they would use the footage and photos that they took during these events.”

Hong Kong activists accused Leeds University of being only “worried about its image” after it contacted them to express concerns about a planned event bordering on university property that was expected to be the focus of a counter-protest by pro-Bejing Chinese students.

In an email seen by the Guardian, the university wrote to the students to insist it was committed to freedom of expression, but the number of people expected to attend the event and the proximity to a road meant “we were not persuaded that adequate arrangements could be made to safeguard all members of our community within the vicinity”.

In Newcastle, about 30 Hong Kong protesters encountered more than 100 pro-Beijing counter-protesters in the city centre, watched over by a handful of police.

One activist who was handing out flyers for the Hong Kong protest told of being photographed and filmed and having conversations with passersby interrupted.

“The mainland Chinese didn’t stop chanting and shouting and even swore at some of us. It was intimidating and hindering,” the student said, adding that the rally had been brought to an end earlier than planned on the basis of police advice.

Other university cities where Hong Kong student activists have complained of being harassed include Reading and Manchester, which has the largest population of Chinese students in Europe. About 5,000 attend the University of Manchester, which has a high profile in China.

Posts on Chinese-language social media platforms by the Chinese Students and Scholars Association Manchester (CSSA-MAN), a network of Chinese students and scholars in the north-west whose website states that they are backed by the Chinese government, have highlighted the location and times of events being held by Hong Kong activists. Counter-protests were also encouraged by the Leeds branch of the CSSA.

Hong Kong activists who took part in a protest on 13 October in Manchester told the Guardian of being filmed and having eggs thrown at them. Counter-protesters waving Chinese flags attempted to drown them out with loud music when they tried to speak to local people.

One activist who attended the protest said they had been receiving “disturbing” messages after the encounter between the two groups. They said: “I am quite intimidated by their threatening behaviour. I think some Chinese students have recognised me even under the mask and proceeded to create fake accounts just for the purpose of anonymous cyber-harassment.”

Applications from Chinese students to study at UK universities have gone up 30% since last year, with numbers exceeding those from Northern Ireland for the first time. The Ucas university admissions agency received almost 20,000 undergraduate applications from Chinese students. The overseas student community is estimated to be worth £20bn to the UK economy.