Jenny's mother Pat knew very little about her own mum's history, except that she had grown up on a Kentish farm, and she and Frances had been evacuated to South Yorkshire during the Second World War.

Pat was naturally curious, but became resigned to her mum's peculiar silence. Frances's secrets apparently went to the grave with her when she died in 1979.

Jenny, who's now 39 and lives in Barnsley, read a magazine article about genealogy research a couple of years ago, and decided to have a go at finding out more of her grandmother's story.

The first few weeks of her search were extremely fruitful.

Using internet genealogy websites, she combed through records of births, deaths and marriages, censuses and other documents such as passenger lists for transatlantic liners.

Her research showed that Frances, born in 1898 in Lambeth, had actually been born and brought up as Eleanor or Nell.

One detail she had given about her life was that she had been raised by a female relative while her own family emigrated to Canada. The 1901 census showed her living in Kent, brought up by a Maria Cheeseman, who proved to be her own grandmother.

Further research uncovered the fact that Frances had hidden for many decades: she had been born in a workhouse, the daughter of a general servant called (Mary) Agnes Wardell, who became pregnant at the age of 27, and presumably lost her job at a house in Clapham.

So far Jenny has not found out who Frances's father was, nor what happened to Agnes, except that she is known to have returned to work, at a pub called The Spotted Dog. Her research into Maria Cheeseman's family has stalled, but Jenny is nonetheless completely smitten by family research.

"You go through a phase of finding things out quite quickly, one after the other. I was obsessed with it all for the first fortnight, and let it take over my life. You get a real buzz...but then hit a brick wall.

"Things have been at a bit of a standstill for about six months, but I know I'll get going again. The beauty of putting details and questions on to websites is that it just takes one person to come back to you with a tiny piece of information to share, and the ball gets rolling again.

"One of the curious facts I found out was that Agnes Wardell's great-great-great grandparents were from Sheffield. And here we are, back in Yorkshire."

Jenny says she has learned from family history research to "expect the unexpected".

She is one of around five million Britons who have uncovered a skeleton in the family closet.

New research by genealogy website www.genealogy.co.uk, shows that one in three British adults has conducted online research about their family in the last decade.

An estimated 1.4 million people have made contact with previously unknown family members, whose existence comes to light via the 730 million UK records held online and
five billion international records.

The most common discoveries are illegitimate children (19 per cent of researchers discover one), family members whose names have changed (14 per cent), family members who were secretly convicted criminals
(7 per cent).

One woman, Shirley Griffin of York, has discovered that her forebear, Frederick Parker, was 27 when he became the last man to be hanged at York Prison in April 1868.

Many people discover a secret adoption within their family
(6 per cent), missing family members (6 per cent) and royal blood connections (4 per cent). Around 23 per cent have confirmed connections to the aristocracy, famous historical figures or rich landowners.

More often, as Newsnight front man Jeremy Paxman found in the popular genealogy programme Who Do You Think You Are?, they find that ancestors have lived in circumstances of unimaginable poverty, unable to feed their many children.

"You really do have to be prepared to find almost anything," says Simon Ziviani, of www.ancestry.co.uk.

"In one case, a person found a triple bigamist in the family – a man who ran three families alongside each other, and presumably did not see that much of any of them.

"He abandoned the three families, having not really been a father to any of his children.

"He then set up home with another woman and became a very attentive father to her kids.

"The other families found out about each other when a member of one of them registered on our website and found that someone else was looking for details of the ancestry of the same man.

"One woman found out that her great aunt was hanged for murder in Canada. She had begun an affair with her married boss, and stabbed her love rival, his wife."

This year, the website launched the records of convicts sent to Australia – one in 30 Brits has a convict ancestor – and First World War pension records.

The Barbados Slave Records, are also online now, having only been available previously at the National Archives in Kew.