AMANDA Redman had no idea what she would find when she went on a dangerous journey into her own family's fraught past, uncovering an emotional story of traumatic upheavals, passionate affairs, long-lost relatives, wife-beating, drunkenness and illegitimacy.

It's enough to make most soap operas look tame, but look at any family history closely enough and you'd very likely find something equally astonishing. Amanda's discoveries are, however, caught on camera in her extraordinary edition of BBC1's Who Do You Think You Are?

"I thought it would be interesting to see where we all came from, but of course you don't know when you start this journey where it's going to take you. It was a complete magical mystery tour for me," says Amanda. "I've always known there were things that my family didn't want to talk about. As kids we would hear the grown-ups talking about something and the minute we would come into the room it was all silence."

With the help of BBC researchers, Amanda was determined to find out what lay behind all the whispers, but first she had to ask her mother, Joan, to agree. "If she hadn't wanted anything to do with it, then I wouldn't have done it, of course" she says.

But there were moments when her questions about family skeletons took her into territory where mum Joan was reluctant to tread, starting with the brutal behaviour of Amanda's hard-drinking, wife-beating grandfather. No wonder she was nervous.

"It was the responsibility that was frightening, because you never know what you're going to uncover. The BBC got as far back as 1066 with our family tree but they were pushing more towards the recent family history, because ancient history would not have any bearing on our lives apart from curiosity. I was frightened that it could get too near the bone," she says.

The key discovery was that, unknown to Amanda, she had a phantom uncle. Her mother and her Uncle Tony had another brother, Cyril, cast out by her grandfather as a boy of ten. Cyril was then raised by his maternal grandmother until, aged 14, he joined the Merchant Navy and was never seen by the family again.

Amanda's mother was born in India, where her mother's father, William Herrington, was stationed with the Indian Army from 1919 to 1939. The Indian Army of the time had a reputation for drunkenness and violence which William did nothing to dissipate. He terrified Joan and her siblings, and his beatings of Amanda's grandmother, Agnes Annie, were so regular and so severe that the Army even offered to send her and the children back to England. Yet she refused to go.

"I was shocked," admits Amanda. "I suppose anybody in this day and age would find it incredibly shocking. I had no inkling at all. He died when I was eight but I didn't ever feel frightened of him. He was scholarly, and heavily into history and Greek mythology. That's really my only memory of him."

But at a time when the Army was holding the line against seething Indian rebellion in the run-up to independence, the pressure on men such as Amanda's grandfather was severe, and he took it out on his own family.

Worst of all, when the family went on a trip back to Falmouth, Agnes's home town, Cyril was left behind, and such was the family's terror of William they never asked why Cyril never returned, or where he had gone. Amanda's investigations reveal the likely reason. Cyril's exact birth date has not been traced, but he was born in 1919, the year William and Agnes married. He arrived before they were wed, and it appears he was not William's son.

"My grandfather kicked him out because he was illegitimate - that's what we assume - and he wasn't my grandfather's child. We don't know whether my grandmother had passed herself off as a widow, because it was just after the Great War so she could well have done that, but it seems he may have discovered something when Cyril was ten that caused him to disown him."

William cut all contact with Agnes's family, the St Legers. No one was allowed to even mention Cyril's name again.

Cyril responded to this devastating blow by becoming a bit of a tearaway. In the programme, Amanda finds a childhood friend of her uncle's who recalls how Cyril and three other lads stole a train, and drove it down the tracks before they were apprehended. Cyril was sent to a reform school.

Then in 1933, aged 14, he joined the Merchant Navy. None of the family heard of him again until now. Amanda discovers that Cyril had a passionate ten-year affair with Hilda Dalton, a married woman in Falmouth, who appears in the programme.

He fathered a son with Hilda, but her husband brought him up as his own on condition that she abandoned her lover. So poor Cyril lost his son as well as his mother, his father and all his brothers and sister. Cyril's son, Derek, later died of emphysema, aged only 48.

Amanda must have felt a wave of pity and sympathy for her long-lost uncle. "Oh God almighty yes... That poor little boy, and for my poor grandmother too, who never got to see him again. I heard from my mother that she used to cry on his birthday every year."

Her grandmother remained incredibly stoical until her death, aged 93, in 1988, but Amanda also made lighter discoveries, including that her gran had been a vivacious young woman whose favourite expression was "Oh la la!"

"I found that even more surprising than the revelations about my grandfather, and rather delightful," laughs Amanda, "because I just remember her as this sweet little old lady who was easily shocked. We called her Bubble because she was like a little round bubble - her feet didn't touch the ground when she was sitting on a chair."

Amanda also discovers that Cyril had another child, Karen, and a family in Liverpool. Cyril died in Karen's arms in 1984 due to bronchial asthma.

There may have been other children too: "We could only trace two, but there's a huge possibility that there could have been more. It was absolutely the norm for seamen to father five or six children in different places; there was no pill in those days."

She also traces the family history back to Ireland, discovering that the St Legers went there in the reign of Charles I but were forced to return in the 1840s because of the potato famine, and she discovers a whole swathe of new relatives in Cornwall.

All outposts of the family meet for the first time in an emotional reunion at Amanda's mum's house in Brighton at the climax of the film, with a tearful Joan and brother Tony seeing photographs of Cyril as an adult for the first time.

"My mother said after the reunion that she thought it had been a very cathartic experience. She had been very reticent about doing the programme but she wanted closure and this was a way of doing it," says Amanda.

"She was very moved by it, and I think it's done her the world of good."

* Who Do You Think You Are? starts tomorrow at 9pm on BBC2. Amanda's edition is on Tuesday, October 19.