A protester says he was not trying to enter Manchester's Chinese consulate during a pro-democracy demonstration that saw violent scenes on Sunday.
Bob Chan told a news conference he was dragged on to the consulate grounds and beaten by men, leaving him with injuries requiring hospital treatment.
It comes after a British MP accused one of China's most senior UK diplomats of being involved.
But consul-general Zheng Xiyuan has denied he attacked the protester.
Amid the growing row, China has claimed there were attempts at illegal entry.
Speaking at a news conference organised on Wednesday by several British MPs, Mr Chan, a Hongkonger, said he was left physically and mentally hurt by Sunday's incident.
He described being beaten by masked men outside the consulate, some of whom he said were trying to take down a display of banners.
"I then found myself being dragged into the grounds of the consulate. I held on to the gates where I was kicked and punched, I could not hold on for long," he said.
"I was eventually pulled onto the ground of the consulate. I felt punches and kicks from several men. Other protesters were trying to get me out of this situation, but to no avail.
"The attack only stopped when a man who turned out to be a uniformed officer from the Greater Manchester Police pulled me outside the gates.
"Let me say it again so I am clear: I was dragged into the consulate, I did not attempt to enter the consulate."
Police in Manchester have said up to 40 protesters gathered outside the consulate - a smaller diplomatic office that is UK territory but cannot be entered without consent.
At about 16:00 BST, Greater Manchester Police said a group of men "came out of the building and a man was dragged into the consulate grounds and assaulted".
"Due to our fears for the safety of the man, officers intervened and removed the victim from the consulate grounds," a statement said.
Mr Chan spoke of his shock at the incident and told of his fear for family members still in Hong Kong.
"I am shocked because I never thought something like this could happen in the UK. I still believe the UK is a place where free speech and protest are basic human rights.
"No amount of violence or diplomatic pressure will change that. I am hurt physically and mentally," he said.
The demonstrators - many of whom were from Hong Kong - were protesting as the ruling Communist Party congress began in Beijing.
In an interview with Sky News later on Wednesday, consul-general Zheng Xiyuan confirmed that he was present at the protest, but denied that he and his staff attacked people.
"I didn't beat anybody. I didn't let my people beat anybody. The fact is, the so-called protesters beat my people," he said.
Footage captured at the scene appeared to show him pulling a protester's hair.
When asked about this, he said he was trying to protect his colleagues who were threatened by the protester, adding: "He (the protester) was abusing my country, my leader. I think it's my duty."
A spokesperson for the consulate had said the protesters had "hung an insulting portrait of the Chinese president at the main entrance".
Beijing later claimed its consulate staff were subjected to harassment and said there were attempts to enter the consulate grounds.
China has "made representations" to the UK government to increase protection for its diplomatic staff.
Meanwhile, the senior Conservative MP Iain Duncan Smith criticised the UK government's diplomatic response to the incident so far.
He told the news conference it had been "wholly inadequate... and I think I'm being slightly kind to them".
Mr Duncan Smith described Foreign Office Minister Jesse Norman as having to be "dragged" to the despatch box in Parliament to respond to the situation.
He said a meeting between the UK and a Chinese official about Sunday's incident resulted in "a gentle rap on the knuckles".
Mr Norman told MPs on Thursday: "Let me be clear: if the police determine there are grounds to charge any officials, we would expect the Chinese consulate to waive immunity for those officials. If they do not, then diplomatic consequences will follow."
A day earlier Foreign Secretary James Cleverly told Sky News the incident was "absolutely unacceptable, that the protests were peaceful and legal".
"They were on British soil and it is absolutely unacceptable for this kind of behaviour," he continued.
Last year, a new visa system gave about 70% of Hong Kong's population the right to live, work and study in the UK with a route to citizenship.
More than 100,000 people have arrived on the new visas, as Beijing's influence over the former British colony increases and following the introduction of a controversial national security law.
After the extraordinary scenes at the Chinese consulate on Sunday, MPs from across the political divide are now pushing for the UK government to take a much tougher stance against Beijing.
The Manchester MP, Afzal Khan of Labour, said the actions of the diplomats had "crossed a red line".
Conservative Iain Duncan-Smith said they revealed the long arm of the Chinese state. He expressed concern that the UK government was being cautious in its response for fear of provoking a "tit-for-tat" from a country with such strong economic clout.
The two agreed - as did Bob Chan - that Britain should expel the men involved, even if prosecutions aren't possible because the attack happened on what is officially Chinese territory.
Greater Manchester Police have appealed to anyone with video evidence to upload it to their website, as they look at images from CCTV, mobile phones and officers' body cameras - part of a "complex and sensitive inquiry".
Sensitive it certainly is - with the impact it could have on relations between Britain and China.
The force says the investigation will "take time", but many MPs says a quick and forceful message needs to be sent to China, as soon as the diplomats involved are identified.