In a taxi on the way to Surrey police headquarters, snow started to fall and the driver was complaining about the night ahead. As we pulled into the driveway of the 19th-century house, with its memorial garden for fallen police officers and a dog training school opened by Bruce Forsyth, I said I hoped his evening improved. “Eva,” he said, gruffly, “We live and then we die.” It was the first jolt of the afternoon, the first time I was left with nothing to say. A crime scene investigator (CSI) showed me inside.

I was visiting the fashion historian Amber Butchart, who had spent the day talking about dead bodies and the clothes they’re found in. We first met in 2002 when she worked as a buyer for vintage clothes shop Beyond Retro. Sorting through old dresses she became interested in what they told us about the past, and went back to university to study history. She hosted a BBC programme exploring the lives of historical figures through the clothes they wore and published books investigating fashion on film and nautical style. Last year Butchart was talking about fisherman’s jumpers on the radio when Dr Karl Harrison, one of the UK’s most experienced forensic archaeologists, was driving home, and he was struck by her explanation of what we communicate through clothing.

“I think like an archaeologist,” he says. “I use buried sequences of material, and this was how she described fashion, and meaning.” He sent her a “very uncrazy email” (he insists) inviting her to meet. He recently gave evidence to the House of Lords select committee on science and technology, impressing upon them how vital it was to maintain a healthy ecosystem in forensics. “Forensic science has become so focused on DNA. I’m trying to retain the importance of… looking at stuff.” Would she be interested, he asked, using slightly different words, in forming the fashion police?

‘Forensic science has become so focused on DNA. We need to retain the importance of looking at stuff’: Harrison and Butchart examine some evidence. Photograph: Pedro Alvarez/The Observer

A body had been found in a field. “It was unclear if it was a shallow burial or he’d died there,” Harrison says. “Soft tissue was lost, but clothes remained. They were out of character – it was a rural location.” Butchart adds: “He was in leisurewear.” By dating the clothes, she was able to identify him from a list of missing people. It was Butchart’s first police job (her title is consultant forensic garment analyst). It was daunting, she says, but fascinating, too. “It’s such an unusual application of what I do,” she says, whose mustard turban and dogtooth trousers mark her out as distinct from the be-fleeced CSIs. “But it felt important. This has more social value than selling old clothes.” She smiles wryly.

Today in Surrey, Butchart has been training investigators in what to look for at crime scenes and how to record it, how to recognise fastenings and fabric in order to date garments, and teaching terminology of non-western dress. “Describe it,” was her advice when discussing the discovery of things such as West African ankara fabric. “Don’t use the word ‘ethnic’, don’t infer interpretation – we need to produce a standardised set of language. One person’s sweater,” she explained, “is another’s jumper.”

I don’t know what I was expecting from a room of CSIs. A sense of urgency, perhaps. Raised voices, rubber gloves, danger. Instead there is tea and a weary whiteboard. The popularity of true-crime literature and TV has created whispering myths around the business of murder, ones that Harrison is keen to dispel. “These aren’t glamorous penthouse murder scenes we’re dealing with – usually it’s cross, injured people whose cars have been broken into. True-crime drama results in expectations of a certain level of science to be applied, not sticky tape and a torch. Everyone expects an easy solution, when, in fact, most of the skills remain intelligence based.” He gestures towards Butchart. In the past he has worked with experts analysing feathers, knots and decomposed tattoos; they both speak calmly and without emotion, careful to be respectful.

“My wife would say I remain a fashion luddite,” Harrison chuckles, “but in my working life, I’m now very aware of what it can offer.”

Fabric of life: a jumper is examined to give vital clues. Photograph: Pedro Alvarez/The Observer

Clearing the home of an elderly woman after her death, her adult children opened a drawer and found the body of a baby, wrapped in clothes. Harrison called Butchart.

“I used the same skills I developed at Beyond Retro,” she says. “I was looking to date clothing, because the older it was, the more valuable.” In the lab, she noted the fabrication. “Heavy polyester, homemade garments with unfinished seams. There was a bullet bra, which I could broadly identify as being from the 1960s, then I looked at the label, researched the company history, the advertising of the manufacturer…” She was able to date the small body “with a certain level of confidence”.

Underwear is a good example of how she applies her expertise. “It dates so well. Foundation garments are worn so close to the body, for one thing, and an offender discarding a body often leaves the underwear on.” And it’s possible to chart its history through fashion. “M&S has a great archive, which is really helpful. From girdles and bullet bras, to more natural shapes with no underwiring, or 90s Wonderbras. Knicker sizes have changed drastically, too – think, for example, of thongs in the 1980s.”

Underwear dates well. Offenders often leave it on a body’

The difference between her work at Beyond Retro and her work with the police is that the majority of cases she’ll work on are dealing with contemporary fast fashion. “And while dress history as a discipline is centred around elite lives,” she says, “I’ve always been interested in everyday experience. Working-class dress was never really documented, in part because it was typically kept until it was worn out. This is about how regular people interact with clothing.” The second difference is the death. “I’m trying to get to grips with imagery of dead bodies.” She winces apologetically.

“Part of my job,” Harrison says, “is teaching people how to deal with bodies. Things like, how to keep a knife in it when transporting it. Which inevitably leads to discussions, including ones about what to do if you’re uncomfortable.” Butchart shifts, slightly. Harrison continues: “PTSD is a risk. It’s 12 years since I worked at crime scenes, but yes, I still remember some. Nobody should have to work under stress, and nobody should feel they have to put a brave face on it. We’re good at informally managing each other’s mental health. We look after each other.” He smiles at Butchart. “The way we all do it, is we tell stories.”

The following day Harrison must finish his report on Grenfell. We put our coats on and push in our chairs. The front reception is locked, so, in the dark we pick our way through the snow round the back of the building, and are greeted by frantic barking. “Semen dogs,” Harrison clarifies, cheerfully, and once again, I’m left briefly speechless. In the gloom, Butchart opens her eyes very wide, and pulls her coat tight. “I feel,” she says, stepping carefully, “very much at the beginning.”