Most of us date our history from the day we are born; for a tiny minority, life begins if they survive being abandoned and are found before it is too late. Tom Jones, whose History is currently on the BBC, was more fortunate: Mr Allworthy "… was preparing to step into bed, when, upon opening the clothes, to his great surprise he beheld an infant, wrapt up in some coarse linen, in a sweet and profound sleep, between his sheets". You’ll find out who Tom Jones’ mother is on Sunday, so I won’t spoil it for you.

For Sandra Webster there will be no such satisfying dénouement. She was found at 6.30pm behind a newspaper office in Kings Cross on 8 November 1955. The doctors dated her birth at around 21 October, and she had obviously been well cared for. She won’t describe what she was wrapped in: "I like to keep something back," she says. "Just in case someone comes forward."

She was adopted, and grew up to qualify as a nurse and marry the boy who lived opposite. The birth of a daughter in 1986 sparked off serious post-natal depression; provoked she believes by unresolved feelings about being abandoned. Since then she has counseled more than 60 fellow foundlings through NORCAP, the National Organisation for Counselling of Adoptees and Parents, which runs a foundling sub-group. "You think you are the only one," she says. "It helps so much to know there are others."

In England and Wales since 1977 babies in this category have been registered separately on the Abandoned Children’s Register after six months to a year of police inquiries. The numbers vary wildly; in the first year there were five. They hovered in single figures until 1983, when they shot up to 16. The late 1980s recession saw a bulge, with a record 18 in 1989. There are slightly more girls found than boys, although whether this is because girls are tougher and more likely to survive exposure, is not known. None have been registered so far this year, but little Catherine Nightingale is set to be the first. At 5.40am on 15 May, an Edmonton newsagent opened his door to bring in the papers. On the step was a holdall containing a very small new-born baby girl wrapped in a tea towel and T-shirt. The newspaper delivery men said she hadn’t been there an hour before when they dropped the papers. Some desperate girl chose her moment – she knew that newsagents open very early.

"We all think she was left to be found," says her case worker Mary Cook. Sandra confirms that very few babies are found in "negative circumstances".

They also think that her mother must have been very young – the evidence being that Catherine only weighed 2.1K in spite of being healthy and full-term. The police came immediately, and the baby was handed over to the out-of-hours social worker who named her Catherine after her first foster mother, and Nightingale after a nearby street. The police carried out an exhaustive investigation including house to house inquiries, but nobody came forward, so she will be adopted in the natural course of things. In Edmonton last year, there was an even less typical case. A young woman admitted herself to the labour ward of North Middlesex hospital and gave birth. She spoke no recognisable language, and while staff were trying to find an interpreter, she vanished leaving her little girl behind.

It is difficult to understand in this liberal age, where illegitimacy and single parenthood carry no stigma, why a mother might abandon her baby. . "At least I can comfort myself that the social climate at the time made single parenthood impossible," says Sandra. "I think today’s abandoned babies will have many more psychological problems as the reasons behind their abandonment must be less straightforward." It is thought that the mothers could be very young, and the pregnancies kept secret - possibly the result of incest or rape.

Today most adoptees can trace their birth parents – although some choose not to. Famous reunions pop up regularly in the papers: Clare Short and Joni Mitchell have both recently fulfilled the standard adoptee fantasy about having special parents. "I feel I am a jigsaw," said one adoptee describing his motives. "All my pieces are there, but the ones at the bottom are blank." Very few are sorry they went through the process, although some are disappointed. For the foundling, there is no trace – the blank cannot be filled. The National Contact Register will not list them because their cases are considered closed - although NORCAP keeps a register of foundlings and will do everything they can to help. "You know nothing about yourself or your family," says Sandra. "For instance, my husband is average height and my elder son is already over six feet tall with size 13 feet. Where does that come from?" For her children, Sandra’s predicament became more understandable when the family adopted a rabbit found abandoned in Luton by the RSPCA.

Dr Malcolm Smith, a Durham University anthropologist, has made a study of historical child abandonment. He came to the conclusion that it was a haphazard business in Britain, but became an institutionalised form of family planning elsewhere – a system which originated in 14^th-century Italy: "Every little town in southern Europe had its foundling hospital," he says. They were equipped with a revolving cradle into which you popped your unwanted baby before pushing it around into the wall knowing that rudimentary care lay within – although mortality rates were high, in some places 100%.

Jean-Jacques Rousseau, the 18^th-century philosopher with revolutionary ideas about natural child rearing, abandoned his five illegitimate children in this way. If you had made a pre-marital mistake in those days in a Catholic country, it might render you unfit to wed. Without the baby, you would be a much more virginal prospect. The poor women who did the wet-nursing had a vested interest as well – their breast-milk became a saleable commodity.

"I wonder sometimes how often my mother has replaced me with other children," say Sandra. "A lot of our sorrow isn’t for us. It is for the woman desperate enough to leave us. They have had to live their whole lives with the guilt, and they will never know what happened to their child."

NORCAP (the National Organisation for Counselling of Adoptees and Parents) can be contacted at 112 Church Road, Wheatley, Oxfordshire X33 1LU