HARD-nosed Newsnight presenter Jeremy Paxman was recently reduced to tears when he discovered the appalling circumstances in which his ancestors lived and died, while tracing his family history.

Indeed, family history sparks all sorts of emotions in even the most cynical of people, says Dan Waddell, author of the second book in the Who Do You Think You Are? series, accompanying the new BBC2 series, in which Paxman appears.

While some believe genealogy to be duller than ditchwater, Dan says it can change some people's lives. ''It's not just about tracing your family back to William the Conqueror and developing this very ornate family tree. There's this image that family history is followed by people who are at a late stage in life.

''One of the things that attracts people of a different generation is this idea that you're going to find out a family secret. Finding out flaws and secrets brings these people to life. There are some people who say knowing about your ancestors makes absolutely no difference to your life,'' he says. ''I don't subscribe to the theory that we are defined by who our ancestors were. We are more than an amalgam of genes passed down to us.

''However, it makes you more humble to know you come from a long line of people who struggled and lived to overcome some very difficult circumstances. It doesn't influence who you are but it definitely influences where you are and how you came to be there.

''You can see who were the movers and shakers in your family and the people who altered their path. In 1850 perhaps your family were living in abject poverty in a slum in a provincial town and yet you might be in a different part of the country in a different economic class. How did that happen?

''Death certificates are fabulous sources of information because they tell you how somebody died - and that can quite often tell you about how they lived. If someone had died of TB in their 30s or died during a flu epidemic you get a sense of how they lived. It brings them to life. It's very compulsive and can take over your life."

In his latest book, Dan gives tips on everything from getting started to how to discover secrets and explode myths in your family tree. Apart from the tearful Paxman, other celebrities who research their ancestry in the new series include Julian Clary, Jane Horrocks, Stephen Fry and Sheila Hancock, whose histories produced some surprising results.

Dan Waddell traced his own family tree for research purposes and immediately discovered a family secret - that his good Catholic grandmother was five months pregnant on her wedding day.

''The problem is, when people discover something like this, how do they present it to their relatives?,'' he says. He did tell his father, who was shocked, but then said that it explained many things about the family.

Of course, the internet has to some extent opened new doors for genealogists - researching a family history is the third most popular pursuit on the internet, behind porn and personal finance.

And discovering skeletons and black sheep is a riveting prospect.

''Few of our ancestors left much of a paper trail unless they stepped outside society's norms and were recognised by the authorities and institutions such as the criminal justice system, asylums, prisons, orphanages and the workhouse,'' says Dan.

Offences such as bigamy were commonplace years ago simply because few people could afford a divorce. While single mothers were outcasts in society, men often celebrated the fact that they were born illegitimately if the father was a person of status.

People should be able to trace their family back to the mid-18th century, he advises, unless they come from nobility, who were very good at keeping records.

''1837 was the year of civil registration, when births, deaths and marriages were recorded by the state,'' says Dan. Before then it was done by local parishes but much depends on how well the churches kept their records.

For those interested, here's a starting point for tracing your ancestors.

FAMILY

* Ask your family for information and record everything they tell you. Ask your relatives to look in their attics to see if there are any heirlooms handed down through the generations. Contact any surviving grandparents, aunts and uncles for clues.

l Try to acquire birth, marriage and death certificates. Old photographs are also useful to find out not only who you get your looks from, but also details of names, dates and places, often listed on the back of the photograph.

l Seek out old letters to glimpse into the lives of your predecessors.

l Is there a family bible? It may have details of who owned it inside the front cover, alongside dates of baptism etc.

l Sketch a rough plan of what you know about your family, placing yourself in the middle, your children below and your parents and grandparents above. That way you can see what you know and the gaps in your knowledge.

BIRTHS, MARRIAGES

AND DEATHS

* If you know where an event took place you can search local indexes at your nearest major library and apply for duplicate birth, marriage and death certificates. Local and central indexes are not the same, so never order a certified copy from the central register using an index reference obtained from the local registry. The certificates will help you understand more about the lives of your ancestors, their occupations, socio-economic groups and their age upon marrying, as well as cause of death.

* Visit the Family Records Centre in London, where national indexes are stored. They can also be viewed on the website www.1837online.com, although you have to pay to see the search results. Another good website is ancestry.com.

* Scottish birth, marriage and death certificates are more detailed. The General Register Office in Edinburgh holds all records. For a fee you can search records online at www.scotlandspeople.gov.uk

l Irish records are held at the General Register Office in Dublin (www.groireland.ie), while all records pertaining to Northern Ireland are held at the General Register Office in Belfast (www.groni.gov.uk/index.htm).

* Who Do You Think You Are? Discovering The Heroes And Villains In Your Family, by Dan Waddell and Nick Barratt (HarperCollins, £14.99).

* Who Do You Think You Are? is on BBC2 from Wednesday at 9pm.

Mike Amos is awa