A secret recording has revealed how a covert police unit in Wales tried to recruit a Black Lives Matter activist to be an informant.

The anti-racism campaigner Lowri Davies shared the recording with the Guardian to raise awareness of what she alleges were “distressing” techniques used to try to manipulate her into providing information to the police.

Davies, a Swansea University law student, is one of the main organisers of a local Black Lives Matters (BLM) group that regularly supports protests about the deaths of black people after contact with police.

She said two police officers spent 90 minutes seeking to convince her to become an informant, imploring her not to tell anyone about the attempted recruitment.

But Davies exposed the attempt by recording a phone call from one of the covert officers. It is the first public evidence that the police have sought to recruit a mole within the Black Lives Matter movement in the UK.

Lawyers representing the activist, who is in her early 20s, have submitted a complaint to South Wales police, arguing that the attempted recruitment was “incredibly frightening and distressing”. Hours after the approach, Davies said her mental health deteriorated.

“If the police are so against racism, like they say that they are, then why are they trying to get informants from groups that are saying that racism is bad?” she said. “If they believed that, they would not be asking me to be an informant, they would be saying ‘we really support the work you do’ and would leave me alone.”

Davies helped set up the Swansea BLM branch as the movement expanded rapidly after the murder of George Floyd in the US by a white police officer in May last year. The non-violent group has supported local campaigns against alleged police brutality and racism.

In March an officer calling herself Rachel Williams called Davies on her phone out of the blue at her home. Davies started to record the conversation soon after it started.

Williams is recorded saying: “Our department, we work with police informants basically. So it could be for a range of different reasons, some persons speak to us because of their involvement with drugs or burglary.” She added: “Obviously, in your case the reason for the contact is because of your involvement with the protests.”

Williams discussed meeting Davies with her superior the following day. Describing herself as not an “overt” police officer, Williams said: “We don’t meet people at police stations, and we don’t meet people at their home addresses, again because of the covert nature of my role. We are not seen anywhere. We would arrange to meet you where we know you’re not going to be compromised, and where nobody is going to see you with us.”

Williams said she wanted Davies to supply information about far-right activists who had protested at Black Lives Matter demonstrations in south Wales. She said she was looking for advanced information about whether the far right could cause violence at anti-racist demonstrations. “It’s that potential for any risk or anything that you could see that could potentially develop … persons turning up who are not for your cause that could cause problems for yourself. That type of thing,” she added.

Davies said this was a ruse to reel her in, as she believes the police would have initially asked her for information about the far-right – which she does not know much about – and then later lured her into giving details about leftwing groups. She described the approach as like “grooming to entice me into being an informant”.

Her suspicion was well founded, according to Frank Matthews, a former Scotland Yard detective who recruited informants for 25 years. “Why would you approach a Black Lives Matter activist for information about the far right? It does not make sense.”

During the phone conversation, Williams verified that she was an officer by reading from a computer details about recent protests Davies had been involved in. Three times the officer implored Davies not to tell anyone else about the attempt to recruit her. She also asked Davies not to bring any recording devices to their meeting the next day, adding: “The only thing I would ask is for you not to tell anybody about this phone call, just to avoid any potential compromise or threat of physical harm to yourself.”

When Davies met Williams and her superior in a car the following day, she said, the two officers checked that her phone was switched off and could not record the 90-minute meeting. The officers drove her around Swansea as they tried to recruit her. She said they asked her about her family and also suggested that she would be rewarded for information she supplied.

Davies said the officers also suggested they were interested in information about other leftwing groups.

The disclosures are likely to heighten longstanding criticism that police in the UK are carrying out unjustified surveillance of political groups that are engaged in democratic and lawful protests.

A judge-led public inquiry is examining the activities of undercover police officers who spied on more than 1,000 political groups over more than four decades. The government was forced to set up the inquiry after a series of revelations about the misconduct of the undercover officers. These included the monitoring of black justice groups, including several run by grieving families whose relatives were killed by police.

As well as deploying undercover officers, police have for years run a secret network of informants within protest groups. Rarely heard about, they are members of political groups who are persuaded by police to covertly supply them with information about protests, often for cash.

Kat Hobbs, of the Network for Police Monitoring, a civil liberties group that has investigated the policing of Black Lives Matter protests, said: “Given the police response to the growing power of the BLM movement, it’s likely that many more people have faced this kind of intimidation and this may be just tip of the iceberg.”

The total number of informants within political groups across the UK is kept secret by the police. Some are recruited through the payment of money. In 2013 an officer offered cash to a Cambridge environmental activist in return for a steady flow of information about students and leftwing protesters. Four years earlier, Scottish police offered to pay the environmental protester Tilly Gifford substantial sums of cash for information about leading campaigners, claiming that: “UK plc can afford more than 20 quid.”

South Wales police said it could neither confirm or deny any details, and it could not comment while the complaint from Davies was being considered.

A spokesperson said: “The use of informants is a well-established and highly regulated tactic used by police forces across the country to protect the public. Their use is controlled within strict legal parameters by trained specialised staff and the accountability and protection of the informant and the public is paramount.

“Protest organisers have an obligation to liaise with police forces, and South Wales police has a proven track record in working with organisers to facilitate lawful protest while minimising disruption to the wider public.”