PETTY thieves, illegitimate children and agricultural labourers. While we all dream of uncovering a member of the landed gentry among the tangled branches of our family trees, these are the kind of ancestors you are more likely to discover.

The parish records and national indexes can contain a wealth of family secrets, hidden for hundreds of years. The majority simply find proof that they are descendants of a long line of peasants.

But for the thousands of people a year who set out to trace their family history, each revelation is fascinating - no matter how small.

"It's like doing a jigsaw," says Olive Howe, of Darlington, who has traced her family back to 1803. "It's detective work and it's very satisfying, you get hooked. When you first start it's really hard work. But I haven't met anyone who hasn't been inspired by seeing their family on a census return dating back to 1841."

Ann Fell, secretary of the Darlington branch of Cleveland, North Yorkshire and South Durham Family History Society, advises people to start by gleaning as much information as possible from relatives who are still alive.

"You need to spend a long time with this stage, finding out as much detail as you can," she says. "Anything you've got in drawers or cupboards, have a look through, and if you've got old photographs, ask relatives to identify who's there. It's no good charging off and thinking you can start looking at census returns straight away."

As a next step, try looking at the National Index, available at most major libraries including Darlington, Stockton, Northallerton and York. Details of births, marriages and deaths dating back to 1837 can be found, but be warned, copies of certificates cost from £6.50.

Parish records are also a valuable tool with the earliest dating back to 1538. They are held in county record offices and some libraries.

But perhaps the most revealing material is found in the census returns, where you're most likely to find the description ag lab - agricultural labourer. They can often be found in local libraries or county record offices by area. The returns are released every 100 years and there are records available from 1841-1891. Family historians are eagerly awaiting the release of the 1901 census on January 2, 2002.

"Just by looking at a census return you can get a whole chunk of information about a family," says Ann. "They are so revealing because they give occupations and you can get an idea of how many people lived in one house, for example."

According to Ann, who has traced various branches of her family tree, including one line back to 1715, you have to prepare for a few skeletons to pop out of the closet.

"You will probably find illegitimacy, and you may find someone has committed suicide, had a mental illness or been in jail," she says. "There have been some families who have found it difficult to accept."

Irene Macleod, of Bishop Auckland, began tracing her family tree 20 years ago and has since discovered a sheep stealer in the family.

"He was stitched up though," she laughs. "I had a relative who was a shepherd and they obviously had a system where the owner came round to check how many sheep they had. They had a swap-lamb system - if they didn't have the numbers, he would borrow six lambs from another shepherd. He got caught in 1870 with some and was sent to jail for five years."

The sentence may seem a little harsh for six sheep, but budding family historians should get used to learning about the harsh existence of their ancestors.

"Some people find it very difficult to accept that somewhere along the line, people have been poor and were in the workhouse," says Olive.

"Extreme grinding poverty is hard to accept."

Irene also made another discovery when she looked up the army records of her great, great grandfather's brother at the Public Records Office in Kew, London.

"I just typed in a name and there he was," she says. "It had information on his eye colour, hair, height and distinguishing marks. I found out he had tattoos - on one arm he had ER, the initials of his mother, and on the other he had the initials of his wife. I also found out he'd had two court martials, but I don't know what for. It was fascinating."

Other vital sources of information can be found in old newspaper cuttings, inscriptions on grave stones and wills. Wills prior to 1858 are held by diocesan records offices and in this area, at York and Durham universities. Later dates can be found at places such as the family research centre at Bolbeck Hall in Newcastle. The Internet is also a widely used tool with some records accessible on line. Historians find it particular useful when searching for any distant cousins abroad.

Tracing your family tree can be a frustrating process with records sometimes mis-filed, or incomplete. In some cases, such as illegitimacy, records were deliberately falsified. But if you hit a brick wall, says Ann, try to think laterally and opt for another line.

"The idea that you can get back to William the Conqueror is not one that I promote. You will probably get back with certificates to about 17-1800s," she says.

And as most enthusiasts agree, family history is a very personal hobby. Says Irene: "You're best not mentioning it at dinner parties because you tend to bore the pants off everyone else."

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FRIENDSHIPS forged at school and college are some of the strongest you'll ever make. www.friendsreunited.co.uk, is fast becoming one of the UK's most successful websites and now contains a database of over 30,000 current and former UK primary and secondary schools, and universities. New visitors are invited to find their schools and add their names and email addresses to the list of former pupils already registered.

Don't miss our weekly Tracer column, if you are searching for details of someone or have a success story to tell. It's in The Northern Echo every Friday.

Write to Lindsay Jennings at Tracer, The Northern Echo, Priestgate, Darlington, County Durham, DL1 1NF or visit the website.