Lost: the thousands of people who disappear in Britain each year

Things don't happen in Stamford without getting noticed. This bustling market town in the heart of Lincolnshire is quintessentially English - it's the close-knit kind of place where people know each other's names and look out for one another. It's hard to believe that one of Stamford's residents could disappear without a trace. But that's just what happened to Robbie Carroll, and no one seems to have noticed a thing.

Carroll was one of the brightest men of his generation: engaging, gregarious and sociable. His only sister, Jane, remembers that throughout childhood he made friends easily, often welcoming new people into his life. Then he went to Cambridge University: "He really got into college life," says Jane, "Acquiring the tweed jacket with patches on the elbow and a professorial air."

"An outing with Robbie would involve afternoon tea and interesting conversation on art or the meaning of life," remembers his close friend Alice Brickwood. Robbie specialised in Italian Renaissance literature and had plans to do his PhD. The route was laid out for a gilded career in academia.

"He certainly had the potential to get a seat as a professor in one of our best universities," remembers one of his tutors. After graduating in the late 1980s Robbie launched straight into researching his doctorate but it dragged on, and years passed without him managing to finish it. He took teaching jobs in Manchester and Dublin and the fast-track to a professorship didn't seem so likely after all.

"The death of our parents really hit him hard," says Jane. "When our mother was diagnosed with cancer Robbie moved back to look after her and that was a really difficult time for him."

The Hole in the Wall pub, just off Stamford high street, was Robbie's local and he was friendly with the landlady, Rachel Wakefield: "He was such a gentle man. But he seemed to have lost his way," she recalls.

After his mother died he went on holiday to the United States, but the trip turned into a disaster. He called his friends saying there'd been fraud on his credit cards. Thousands of pounds had been spent and he didn't know how.

When he got home he called his sister and said he needed to get a job - any job - and get a structure to his life. Jane thought this was positive: he was starting to sort his life out.

"I think about it now and maybe he was just telling me what I wanted to hear," she says.

In late March 2006 he hadn't been seen around Stamford for a few days. It was unusual not to see him at the Hole in the Wall enjoying his regular glass of wine, so Rachel went round to his house to check he was OK. When she got there, she found the back door unlocked and his computer left on.

"It was as if he'd just popped out to the shops," she remembers, "There was a stack of unopened letters on the front mat."

No one saw him leave and there's no clue to where he might have gone. Over the past year it's emerged that many of those letters were demands from banks and loan companies he'd borrowed from.

"It was as if he was living a Walter Mitty-type existence," says Jane. "Maybe he just needed to escape, go somewhere and start again. I look at the faces of men selling the Big Issue and think 'That could be my brother'. We miss him very much. His nephews remember Uncle Robbie. We want him to come home and be part of our lives again."

Robbie Carroll's story is just one of many similar troubling tales. In Britain, a staggering 210,000 people are reported missing every year, and, though the majority turn up within 72 hours, the National Missing Persons Helpline takes on 10,000 new cases each year.

Over the last nine months I've been working with a team making a series called Missing for the BBC, travelling around the country meeting parents whose children have vanished. Many report that their loved ones had been struggling to hold a lid on difficulties in their lives, and speculate that something may have acted as a trigger that made them feel they just had to leave.

Initially, when someone is reported missing, the police will investigate - there are teams of officers across the country dedicated to such searches. Longer-term missing cases are taken up by the National Missing Persons Helpline (NMPH), a charity set up after the disappearance of Suzie Lamplugh, the young estate agent who vanished in July 1986. The work of the NMPH is crucial. It launches nationwide publicity appeals and gives support to the families, as well as offering help with the ongoing investigation. The charity resolves 70 per cent of cases they work on.

Until now there has been no centralised register of missing persons, but in December 2006 the Association of Chief Police Officers signed a National Protocol Agreement with the NMPH. Under this agreement, information will be shared much more widely, which should lead to swifter resolution in many cases - and less protracted agony for the families involved.

Because no matter how long a person has been missing it doesn't get any easier for the people left behind: the pain of not knowing what has happened is almost tangible; there's an emptiness in their eyes. As one mother we met put it: "I know it's a terrible American expression - but we just want closure."

Missing: Tom Moore Last seen Brentford, 1996

The Moore family live on a picturesque square in Brentford, Middlesex; it was the location for the filming of Finding Neverland. Tom's father was an officer in the Marines, his mother a teacher. Tom, the second child, was very close to his older sister, Diana, and younger brother, Ben.

"Tom was a very sensitive and deep child," remembers his mother, "At primary school he put his hand up and asked whether Romeo and Juliet would go to hell because they had killed themselves."

He was bullied as a teenager and found comfort in religion, reading the Bible for hours. A trip to Goa during his gap year seemed to compound his anguish when he had a bad experience with drugs.

At the age of 21 he was diagnosed with schizophrenia. Young people with the beginnings of mental-health problems are more prone to recreational drug use. It's part of the social-drift effect that starts to push them to the margins of society. For a year Tom was under constant medical supervision and his mother remembers this as his most stabilised time. His sister and brother aren't so sure. They saw the dulling side-effects of the medication.

"It was like the fire of his personality was doused," says Diana. "He was sedated, but not the Tom we knew."

There's a lot of research into the prevalence of mentally ill patients self-medicating with recreational drugs. Dr Paul Keedwell, consultant psychiatrist and clinical lecturer at the Institute of Psychiatry says: "The link between cannabis use in adolescence and increased risk of schizophrenia is well established. The use of cannabis exacerbates the symptoms in the long term and makes the illness more resistant to conventional treatment."

Up to 20 per cent of people who go missing have mental-health problems. For over a decade Tom struggled with his illness and his medication, and by the late 1990s he was travelling abroad for months at a time. He went on pilgrimages to places like Lourdes and Medjugorje in Bosnia. His Christianity became the focus of his life.

Every time Tom returned home, his family welcomed him back. But one afternoon in July 2003 he emerged from his bedroom and went into the living room where his mother was teaching. He waved goodbye to her. She thought he'd be back for dinner. But this time the manner of his leaving was different. He left a note saying: "I may be some time."

A month after he left, a bank statement arrived at his home showing a withdrawal in Italy. It prompted Tom's brother, Ben, to start his own search. He travelled with their father across Europe, trawling hostels and religious sites with photos of Tom. At a monastery in northern Italy they got a positive sighting: a friar was convinced Tom had been there just two weeks previously.

"It was frustrating to think we'd missed him," says Ben, "but it also gave us renewed hope that he's possibly living a monastic life and that one day he may come home."

"It can be very hard for a family to hear, but every adult has the right to go missing," says Paul Tuohy, the chief executive of the NMPH. "Sometimes we are able to find a person, but if they don't want to be found then under data-protection laws we cannot tell the family. We can try to pass on a 'safe and well' message. This can at least alleviate some of the heartache and uncertainty."

The Moore family is still hoping for that message.

Missing: Sarah Flooks Last seen Found dead in 2007

Sarah Flooks and her five siblings were brought up in rural Somerset, with deserted beaches as their playground. In the late 1970s, she moved to London where she met John Mouzouros, the man who was to be her partner for the next 30 years. She trained as a teacher and found work in an east London primary school. "Sarah was so respected and dedicated," says headmaster Bob Henney, "She set up the nursery school, building it from scratch."

Sarah and John loved travelling and took adventurous holidays. Although her work was pressurised, John thought that she was taking it in her stride.

In March 2006 Ofsted gave Sarah's school a few days' notice that it was to be inspected. Sarah confided in her mother, Dorothy, a former teacher, and told her she had done all she could to prepare. "The night before the inspection Sarah arrived home late," John recalls. She had something to eat and got ready for bed. John was at his computer and he took a picture with his webcam as Sarah stood over him looking at what he was working on. It's the last photo of them together.

John didn't hear Sarah leave the house the next morning but he got a call from the school before 9 o'clock asking where she was. The inspection was about to start and she had not turned up. John walked her route to work but there was no sign of Sarah or her car. He thought she might have driven to Somerset to see her mother.

"Every car that went down the road, I thought it was her," remembers Dorothy Flooks. By the end of the day she hadn't arrived so the police were called. Back in London, two days later, it was John's father who discovered Sarah's car, parked in a nearby road. Two witnesses, who knew Sarah, reported seeing her walking along a muddy bank on the morning of her disappearance. The focus of the police search became Wanstead Park. Despite using tracker dogs, helicopters and infrared heat-seeking devices, the police investigation found few clues to Sarah's whereabouts.

A couple of months after Sarah went missing, John discovered a diary in a drawer. It was an insight into her great inner turmoil: she was worried about turning 50, her job and how much longer she could "stick it out".

In January 2007 Sarah's body was discovered in woods in Wanstead Park, less than a mile from her home.

Sarah's funeral was a humanist service. The children from her school made tissue-paper flowers with messages attached. One read: "Miss Flooks you always kept a secret."

Her family are now waiting for the inquest. They wish they could have had more answers. They are putting a bench on cliffs overlooking a beach in Somerset as a lasting memorial to Sarah's life.

Missing: Anne Simpson Last seen Skegness, 2004

Skegness is known as a happy east coast seaside town. It's home to one of Britain's largest holiday camps and to 100,000 mobile homes. It was where Anne Simpson lived with Tom, her partner.

Anne had brought up her five daughters in Leicester as a single mum. She was a gregarious and exuberant lady who did all she could for her family. Tom remembers the evening they first met in the pub. He was playing cards and losing. Anne came up to his table, picked up the five-pound note he'd just bet and said, "I could feed my family for a week on that."

In 2001 her daughter Jenny was diagnosed with breast cancer. Initially the treatment seemed to be working, but then the cancer returned and in 2002 Jenny died.

Anne struggled to come to terms with the loss. Tom remembers how hard it hit her: "She was someone who believed a parent should not outlive their children."

After Jenny's death, Anne lost a lot of confidence and found it difficult to go out in public. Leicester had a lot of painful memories and although her family was nearby, she decided to move away with Tom.

They hoped Skegness would offer a calmer pace of life. Anne started to rebuild her confidence. Her daughters and grandchildren would visit regularly and on 25 September 2004 they came for the weekend.

They went to the fun fair and walked on the beach. On Sunday evening, after she'd said goodbye to her family, Anne went to the pub. The landlord remembers her because of the group of people she joined.

"She was this older lady with silver hair sitting with a group of heavy-drinking biker types. It was all very lively."

The next morning Anne was not at home. Tom noticed that the medication she took for diabetes was still on her bedside table. He immediately called her family and the police. The Coastguard launched a massive land and sea search. Lifeboats and helicopters with heat-seeking equipment were scrambled.

Lincolnshire Police conducted one of their biggest missing-person investigations ever, but there have been no sightings.

It's thought that the bikers drinking in The Bell pub on 25 September 2004 are the last people to have seen Anne. Police would still like them to come forward with anything they can remember about that evening.

Missing: Barry Coughlan Last seen Crosshaven, 2004

There is just one road into Crosshaven, a sleepy fishing village like dozens of others dotted along the coast of southern Ireland. The same families have lived there for generations and everyone knows one another. The Coughlan family is at the heart of the community. Barry and his sister, Donna, were always very close, and shared the same circle of friends.

Barry lived for fishing; his ambition was to work as a deep-sea fisherman. In April 2004, at the age of 23, he landed his dream job - on a trawler. To celebrate he bought himself a new car, a red Toyota Corrolla. He had the weekend off to relax before going to sea. On Friday he drew €200 out of his Post Office account

On the evening of 30 April 2004 Barry drove to his local pub. On the way he popped into a friend's house. The landlady of the Moonduster remembers him coming in: "He was relaxed and normal. He had a couple of drinks and chatted with the locals. We closed around midnight and he left alone."

The next morning Barry had not returned home and his mobile phone was in his bedroom. His phone was bleeping with messages. When his parents realised he wasn't with any of his friends, they called the police.

Two witnesses came forward who had seen him walking across the pub car park to get into his car the previous night.

The search for Barry covered the whole of Ireland. Police went through ferry passenger lists, and divers searched the waters around Crosshaven. There was not a single sighting of Barry or his car.

His disappearance has deeply affected the whole community and there will always be a place for him on the trawler he was going to work on.

As the third anniversary of Barry's disappearance approaches, it's still no easier for his family. His sister has lost her best friend and his parents only get through each day by telling themselves this could be the day the phone rings.

'Missing' will be broadcast on BBC1 from 16-27 April, from Monday to Friday, at 9.15am