Extraordinary evidence has emerged that the Metropolitan Police targeted a Chinese dissident in London following concerted pressure from Beijing.

Shao Jiang, a Tiananmen Square survivor who fled China and was granted political asylum, was arrested in London in October 2015 during a state visit from President Xi Jinping.

Video footage shows Shao holding two A4 sheets of paper, one saying “End Autocracy” and the other saying “Democracy Now” before being aggressively detained by officers.

After being taken to a local police station for a breach of the peace the 52-year-old was subsequently arrested for conspiracy to commit a section 5 public order act offence. This is a more serious charge that then enabled officers to search his London home, seizing computers which Shao suspects may have been given to Chinese authorities before they were returned to him.

Police watchdog investigators then found evidence that the Met’s treatment of Shao, one of the last protesters in Tiananmen Square in 1989, was influenced by pressure from Beijing to ensure Xi was not “embarrassed” by protests during his visit.

Following Chinese pressure, documents show UK government officials, understood to be from the Home Office, also made “unusual requests” to the police about managing the state visit, an intervention that one officer described as “unprecedented”.

Investigators from the Independent Office for Police Conduct (IOPC) found proof that demands from Chinese officials, including its security service, may have informed the decision to arrest Shao for conspiracy. “There is evidence to indicate that these requests, together with their consideration of the ongoing risk to the CSV [Chinese state visit] and to Shao’s safety, thereby influenced the decision to arrest Shao for conspiracy,” stated an IPOC report.

Speaking for the first time about the incident Shao, who escaped Hong Kong before its handover to China in 1997, told the Observer: “I expected so much more in a democratic country. We are now confronted with the chilling reality that we live in a country where the suppression of peaceful protests has greatly undermined the fundamental values of its own civil liberty and democracy.”

The revelations of political pressure emerged during an IOPC investigation into Shao’s arrest. Last Wednesday the watchdog announced that police officers questioned over the arrest will not face disciplinary action.

Yet it has also emerged that the IOPC completed its investigation into the treatment of Shao in June 2018, finding then that Met officers had a case to answer for gross misconduct.

The Met responded to the misconduct verdict and, despite no new evidence emerging, the IOPC completely reversed its decision and found no case to answer. Emily-Jade Defriend, a solicitor for the law firm Bindmans who is representing Shao, said: “This is completely unacceptable conduct by a regulator which holds itself out to be an independent watchdog of the police. If the IOPC is unwilling to stand by its findings after a lengthy investigation, then it simply isn’t fit for purpose.”

Facebook Twitter Pinterest A still from the video of Shao Jiang’s arrest in London for protesting during President Xi’s state visit in 2015. Photograph: Tibetan Community UK/PA

Shao, a PhD researcher on democracy, condemned the regulator’s U-turn as “morally wrong and procedurally incorrect”.

Although significantly redacted, the IOPC report refers to a letter from a Met silver commander, who coordinates public order strategy, that “included a list of the ways the Chinese delegation had tried to apply different types of pressure to both silver and more widely, the MPS [Metropolitan Police Service].”

The commander, in daily contact with the Home Office and Foreign Office before the visit, told investigators of “unusual requests from the UK government in respect of managing protest during the CSV and in their experience this was unprecedented”.

Two senior officers from gold and silver command, along with the head of the police powers unit within the Home Office, added that planning meetings were “not without difficulty” and hinted there was evidence to suggest both Beijing and UK government officials were to blame.

Defriend said: “It is impossible not to conclude from the findings of the report that political pressure was a determining factor in the arrest.” Following the decision to arrest Shao for conspiracy, his home was searched and his laptop, USB stick and other computers were seized. Although no definitive proof has emerged that these items were passed to Chinese officials before they were returned, Shao received a warning from Google that a “state actor” had attempted to access his accounts.

Arresting Shao for conspiracy meant he could receive bail conditions, which prevented him protesting within 100 metres of the Chinese president.

The suppression of peaceful protests has greatly undermined the fundamental values of civil liberty and democracy Shao Jiang

The arresting officer, a superintendent, did not witness Shao’s breach of the peace arrest and IOPC investigators were unable to ascertain how he obtained the information that led him to believe Shao had committed the conspiracy offence. The officer refused to answer IOPC questions about the case, which was eventually dropped because of no evidence.

The revelations follow intriguing details of a bad-tempered meeting at the Foreign Office’s Lancaster House in the hours before Shao’s arrest with Chinese officials over security arrangements for the state visit.

The episode prompted police commander Lucy D’Orsi to later reveal the Chinese delegation “walked out of Lancaster House and told me that the trip [state visit] was off”.

D’Orsi said: “The assertion that political manipulation of the command team or, indeed, the broader Metropolitan Police took place is wrong and doesn’t reflect the facts. The policing of the state visit was a matter for the MPS. Any other suggestion is wrong.”

The IOPC said that initially investigators believed officers had “breached professional standards” but detailed analysis of the evidence led them to feel that “no officer had a case to answer for misconduct or gross misconduct.”