When Gary Collins arrived at work in Stoke Newington police station, east London, in January last year he was told a teenage boy had been stabbed to death. Jeremie Malenge, 17, was found slumped on the road with stab wounds in his chest. There was CCTV footage of the boy being chased by three figures wearing sports clothes. After they saw the video, the murder investigation team called Collins.

The 48-year-old police officer is wirily framed and casually dressed. He grew up in Hackney; as a teenager he never imagined he was going to end up in the police force, but he has been an officer for 21 years. His speciality is identification. “I get called up all the time,” he says. “I’m usually the person who is shown images first.” We are in a bland-looking council building near the town hall where Collins works as part of the Gang Unit.

After the Malenge murder the investigation team drove him to Hackney Central station. They led him into a cubicle and showed him CCTV footage of the suspects running through the station. It was poorly lit and the attackers were a shadowy blur, their faces largely obscured. Collins studied the video and immediately identified two of the figures, from memory, based on the few facial features he could make out. The third figure also looked familiar. Later that weekend, Collins was watching a rap video on his mobile phone (many of the characters he ran into on the street made rap videos) and realised one of the men in the video was the third figure in the footage. When he returned to work he supplied the third name. Detectives quickly found and charged the three men Collins had identified – and a woman who had not appeared in the CCTV footage – with murder. They went on trial at the Old Bailey that July. Collins gave evidence and was cross-examined regarding his identifications. On 21 August 2015, the jury convicted all four suspects of murder; the following month they were all sentenced to between 12 and 18 years.

Collins had realised soon after joining the police force in 1995 that he had a particular gift. “I was very good at looking at pictures on walls and going out on patrol and saying, ‘That’s that person.’” He recalls “stopping people once and remembering them years later”. While working with the Gang Unit, Collins would patrol the streets encouraging young people to steer away from crime. “I know burglars, drug addicts, pickpockets; people from all walks of life,” he says. That street knowledge became particularly helpful following the London riots in 2011. “I was off at the time,” he says, “but I was watching Sky News and I immediately recognised some people.” Collins cut short his holiday to go into work and was tasked with identifying the rioters. “I spent six months going through the CCTV,” he says. “The figures in the footage would often have their faces covered – there were lots I identified just by their eyes.” Collins eventually named 190 people, the most identifications by any one officer in the Metropolitan police. Some 90% of these were made from street knowledge and memory.

Carla Snook: ‘One day one of my colleagues said, “Mate, you’re really good at this – I am going to flag you up to the Met.”’ Photograph: Manuel Vazquez/The Guardian

Most of the people that Collins identifies in Hackney are young men he has never met but seen only on screens. He often sees them in the flesh for the first time when he provides testimony in court. “I was in court the other day and the defendant was sitting close by with his barrister,” he tells me, “and he asked who had identified him. The barrister pointed at me and the guy said, ‘Who the fucking hell is he? I don’t know him!’”

The news of Collins’ success brought him to the attention of Mick Neville and Paul Smith at Scotland Yard. Neville had researched the use of CCTV in the court system and discovered that it was very poorly used by the police. This prompted him and Smith to set up a special unit to collate and share images of unidentified criminals. Next they had to find officers who could help them sort through the images. During the riots certain names kept recurring, of officers who were recognising more people than any of their colleagues. Smith and Neville visited police stations, holding open surgeries to ask which officers were making the most identifications. “Some officers were making one or two,” says Smith, “and others were making repeat identifications week after week.”

Carla Snook was one of those officers. She is 39, cheerful and bubbly, with straight long blond hair. When she was a young girl and went on holiday with her family, Snook would be convinced she was spotting children who had gone to her school. “But they didn’t,” she says, “it was people I had seen at the airport, or in fleeting glances on the beach or on the plane. I would mention it to my parents and they would think I was crazy.” Snook joined the police force 13 years ago and worked in Belgravia, west London, on the Safer Neighbourhoods intelligence desk. She would often look at Caught On Camera – a Met publication featuring images of unidentified suspects that is released on the intranet and displayed around police buildings. Snook would regularly recognise people on the list. “One day one of my colleagues said, ‘Mate, you’re really good at this – I am going to flag you up to the Met.’” Snook met Smith, who told her he was setting up a special unit of police officers with extraordinary powers of face recognition. Did she want to join?

He looked a bit iffy so I told my children to stay close to me.' A week later Snook got an alert. She knew it was him

The Super-recogniser Unit is based on the third floor of a grey stone police building in Lambeth in south London. It is the only unit of its kind in the world. It was set up in May 2015, and moved from Scotland Yard in July; the charts showing the criminals they have identified and cases they are currently working on are still to be unpacked. The team consists of six officers – five men and one woman. Snook is usually at her desk by eight in the morning. “We are all quite driven,” she says. “We would much rather sit there and try to find these people than go home – we’re a bit sad really.” Alongside the super-recognisers working full-time in the unit, there are around 150 working in police departments across London. (Smith wanted Collins to join the unit, but his borough refused to release him: he was too valuable.)

Since it was established, the unit has made 2,250 identifications. “We account for just under a quarter of all identifications within the Met,” says Eliot Porritt, the 36-year-old former beat cop who heads the unit, “which is crazy because there are just six of us – and 32,000 officers.” This success has drawn police forces from around the world to London. After hundreds of women were sexually assaulted in a mass attack in Cologne on New Year’s Eve, the German police invited the London super-recognisers to assist them. Porritt and Andy Eyles, who joined the Met 10 years ago and has been with the unit since last winter, spent two weeks in Cologne. They studied the video footage and gave advice on how the authorities could use CCTV more effectively. “They had previously been using the CCTV to find the suspects,” says Eyles, “but our suggestion was to follow the victims – then you would see the suspects coming up to them.” They also identified and mentored three German officers who potentially had enhanced identification skills.

Ten super-recognisers were deployed in the inquiry into the murder of Alice Gross. The 14-year-old went missing as she walked along a canal towpath in August 2014. The 600 police officers who joined the search for her made the Met operation the biggest since the 7/7 bombings. One of the team from Neville and Smith’s unit examined the grainy footage of Gross as she walked along a canal. He noticed a man on a bicycle following the same route 12 minutes later. They tracked the man via CCTV as he disappeared into an off-licence and cycled to the river Brent. The next time he was spotted on camera was later in the evening, dressed in different clothes. This prompted a fresh search of where the man had been seen and that eventually led to the discovery of Alice Gross’s body. The man was later identified as Arnis Zalkalns, but by the time police found him he had hanged himself.

Andy Eyles: ‘My wife would say I had a really good memory, but I just thought hers was rubbish.’ Photograph: Manuel Vazquez/The Guardian

One of the key tactics for the team is linking offences together, which they call “snapping”. “We will go into the database and put in a description of, say, a white male with a bald head and glasses,” says unit coordinator Smith, “and then the super-recognisers will go through the images and when they think they have seen the same person they will start linking them together.” The more crimes that can be connected, the longer the potential sentence. For example, Austin Caballero had 40 convictions for shoplifting, totalling more than £100,000 of luxury goods, and also one count of racially aggravated assault. He was sentenced in April to three and a half years for the thefts and an additional three months for the assault. Michael Prabucki was sentenced in August to four years’ imprisonment for 39 convictions for shoplifting. And Neville Stanbury was sentenced in October to four and a half years for 40 offences after the super-recognisers made 31 identifications. Each unsolved crime was a failed case that had been shut down until the unit linked them to the same person.

The team also attend major concerts to ensure known thieves do not gain entry. “They have images [of suspects] stored in their brain,” says Smith, “and they go to the concert and stop them from getting in. Arctic Monkeys got hit for 140 phones on one night; in London we did two nights, and during those two nights five phones were stolen.” Pete Williams, a greying, quietly spoken 40-year-old member of the unit, was instructed to attend a Libertines gig. “There was a small, organised gang who had been following the band around Europe and stealing phones,” he says. “We had been given images of those people and were at the front of the security, stopping several people. Crime was pretty much nil that night.”

We get obsessed with our jobs. I am quite happy going through 20,000 images looking for a distinctive earlobe Andy Eyles

Andy Eyles was a police officer working in south London, interviewing people in custody, when he was called to join the unit. He is 36, and shaven-headed with a five o’clock shadow. Before he joined the Met, he used to run pubs, clubs and restaurants. “I would remember that someone came into the pub three months ago,” he says. “My wife would say I had a really good memory, but I just thought hers was rubbish.” He says he enjoys staring at a screen for 10 hours a day. “We get obsessed with our jobs. I am quite happy going through 20,000 images looking for a distinctive earlobe.”

The ability to never forget a face may be immensely helpful in fighting crime, but it means super-recognisers are never off-duty. “I will be walking with my wife and kids and be saying, ‘He’s a druggie, he’s a shoplifter,’” he says. “And my wife will say, ‘We were having a nice day out and now we are surrounded by criminals.’”

Recently, Snook was in King’s Cross station with her children when a man walked past. “He looked a bit iffy, so I said to my children to stay close to me,” she says. One week later she received an alert about a high-risk missing person. She knew from the picture it was the man she had seen. She called the Missing Persons Unit and told them she had seen him the previous week. “The woman on the phone was a bit blase and I am not sure she believed me,” says Snook, “and then I told her I worked at the Super-recogniser Unit.” Within an hour British Transport police had located the man.

“I am always jumping off buses and trains because I have seen someone,” Collins says. “I was coming back from court and I saw someone who was wanted for seven offences. Once I had to stop the car three times – I would take one person in and then on the way to the station I saw someone else who was wanted, so I picked them up, and then as we were driving I saw someone else.” This degree of commitment can be mentally draining. “I have found that since doing this my short-term memory is just diabolical,” says Snook. “I guess all my brainpower goes into remembering faces. I was taking the tea and coffee orders recently and by the time I got to the kettle I had forgotten them.”

James Rabbett joined the Super-recogniser Unit after winning awards for being the highest arresting officer in the country. Photograph: Manuel Vazquez/The Guardian

Is there anything different about the brain of a super-recogniser? One autumn afternoon, James Rabbett, 35, travelled from Scotland Yard’s offices to the University of Greenwich to find out. Rabbett joined the Super-recogniser Unit after winning awards for being the highest arresting officer in the country, making 200 arrests in just one year. Rabbett was met at the university by Dr Josh Davis, who has been researching super-recognisers since 2008. Davis and his assistant led Rabbett into a ground-floor room where they pulled a pale blue rubber hat that looked like a swimming cap over his head. The cap had sensors attached that measured electrical activity from different parts of Rabbett’s brain. He was then shown two series of 20 images and asked if any of the original images were repeated. This was done with seven batches of images.

Rabbett then went into another room and sat behind a computer screen. He was shown photographs of eight people with one page per person. On each page the people were shown from various angles and distances, wearing different clothes. The research assistant explained that Rabbett would be shown a series of video clips and should look out for the people on the pages. They might appear once, twice or not at all, and he had to say how sure he was. The video was 18 minutes long.

The first scene was people walking along a riverbank towards and away from the camera. Rabbett studied the photographs on the sheets of paper, one by one. He watched attentively and then stopped the video. “I would say this is my first sighting,” he said, “this girl here. I am saying it is her based on her hair, she has quite a long face and a big nose. If you look at the line of her eyebrows, I think her left eye is slightly lower than her right, so for me that is my first call.”

The brains of super-recognisers appear to process certain information faster than the rest of us

The second clip was from a shopping street. He eventually stopped the film and held up a photograph of a woman against the screen. “The jaw line is very strong, a high hairline combed the opposite way to the photograph, but you can see it is quite high. The eyes are quite close together.”

Davis describes what was going on inside Rabbett’s brain: “We are finding differences in brain patterns. It is about the speed of responses.” The brains of super-recognisers appear to process certain information faster than the rest of us. Davis also says that there is some suggestion that “one part of the brain, known as the fusiform gyrus, which seems to be specialised for the processing of faces and to some extent other images – that bit tends to light up for faces more than other objects.”

The term “super-recogniser” was first used in a study published in 2009 in Psychonomic Bulletin & Review. The authors focused on four case studies who seemed exceptionally good at remembering faces. The study suggested that super-recognisers represented the extreme opposite to prosopagnosics – otherwise known as people with face blindness. The authors suggested that just as prosopagnosia affects 1-2% of the population, it was reasonable to assume that another 1-2% were super-recognisers. Those in the unit that Davis is testing are among the top 1% of that group.

At present, the police get only 5% of identifications from members of the public; are there citizens out there with these talents who could help the police? “We may start using a mixture of civilians and officers,” suggests Porritt, “because there may be people out there with wild talents for this. There is no reason they could not come along and make the initial match, and then we do all the stuff that requires a warrant.” One police force has suggested testing those in Neighbourhood Watch schemes. Using more super-recognisers, claims Davis, could “reduce crime in the first place because if you think you are going to get caught on camera there is a massive incentive not to commit a crime.” Collins is not convinced. “Would it stop them committing crime?” he asks. “Possibly, or maybe they would just cover up more.”

Eliot Porritt: ‘There may be people out there with wild talents for this.’ Photograph: Manuel Vazquez/The Guardian

Of course, super-recognisers are not super-human: they do sometimes get it wrong. Identifications alone are rarely used as evidence; they are usually a starting point for police to find witnesses or supporting forensic evidence. “We are not infallible,” says Porritt. “But what does seem to be the case is that super-recognisers get it wrong less often.”

The success of the super-recognisers relies not only on their innate abilities but also on the ubiquity of CCTV. There are thought to be around 400,000 CCTV cameras in London and more than 4m across Britain – and that doesn’t include private recordings from cameras in businesses and homes.

In April, Hampshire police asked for help investigating a brutal hammer attack on a 17-year‑old girl. Snook and Williams were sent to examine CCTV footage. Mobile phone data had led them to a particular street, which then gave them an image of a suspect. What they needed to do was find him in other footage that would help identify him. “It was my first big deployment,” says Snook, “and it was for a really horrific crime by someone who was previously unknown.” Working together, and watching hours and hours of video, they were able to locate the suspect in a car park and track him to his car. This gave the police a registration plate; they managed to arrest him as he was getting into the car. The man, James Hemming, had never been arrested, but his DNA matched that found at the scene. Hemming pleaded guilty in early September to wounding with intent to cause grievous bodily harm. He will be sentenced in December. “That was really fulfilling,” says Snook. “I get such satisfaction out of identifying someone who thinks they have got away with a crime.”

Porritt and Smith would like all new and existing police recruits to be tested for their facial recognition skills. “In 1902, when fingerprints were first used to solve crime, there was a lot of scepticism,” says Smith. “I believe super-recognisers are the way forward.” If about 1-2% of the population have super-recogniser ability, and there are roughly 48,000 officers and police staff in the Met, “we have 480 super-recognisers lurking around that we need to find”.

Snook has some ideas about where to find the next generation of people-spotters. As a girl watching television with her family, “I would say, ‘That’s so and so, and he was in the other show,’ and they would say, ‘How do you remember that?’” she recalls, “and I would say, ‘I remember his face.’” She now has two young children aged five and six. “My daughter will point out people we have seen out shopping,” she says. “We might have seen them days earlier in another part of town. And when they are watching the TV they do exactly as I did. It freaks me out.” Snook told Davis, and she has given permission to have her children tested. She knows that one day they will be asked the same question she has been asked so often, and she knows the answer she will advise they give. “When people ask how I do it, I just say I don’t know,” she says. “My brain just does it – does yours not?”

• Are you a super-recogniser? Take the University of Greenwich super-recogniser test: goo.gl/V5mMGV