A LARGE number of people will assemble at Glasgow's SECC next weekend to find out more about themselves.

The occasion is Who Do You Think You Are? Live, an offshoot of the BBC series, which has engrossed millions of viewers and nurtured a booming genealogy industry. The event promises to be a "gathering of like-minded people in pursuit of roots", according to Else Churchill of the Society of Genealogists, with advice, specialist resources, exhibitions and workshops. It is suitable for beginners or those already at the genealogy-face who have hit a brick wall and need a one-to-one session with an expert.

My interest in scrambling up the family tree was sparked by a desire to know more about my grandfather John Shields, who was killed in the First World War. Family research had already established that a Charles Shields and his wife, Bridget, had come to Glasgow from Ireland around 1840.

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My first stop was the Government website Scotland's People, which is free to join. You buy credits (£7 for 30) and play a form of genealogical online gaming. It costs one credit to look at search results narrowing down your options and five credits to print out what you hope is the right census page or birth, marriage, and death certificate.

Becoming ever more addicted to the habit, I took out a subscription to Ancestry.co.uk, which lets you hack around census and other records at no extra cost. You build and store the family tree. The site directs you to hints from other members' research. This can be misleading. Some enthusiastic American researcher had one of my great-great grannies having babies simultaneously in Ireland and Scotland.

Amateur genealogy should come with a health warning. It can become an obsession. There will be long, late-night online sessions followed by early morning sessions, which may interfere with real life. When you try to relate to nearest and dearest the fascinating information you have uncovered, the response may be: "Gonnae just leave your ancestors in peace?"

Much of the detail uncovered will be mundane but there may be what Else Churchill refers to as Who Do You Think You Are? moments. Like when actor Alan Cumming discovered his war hero grandfather had shot himself playing Russian roulette. Or when Jeremy Paxman was reduced to tears on hearing of the dire poverty of his great-grandmother in the east end of Glasgow.

The closest I got to such a moment came when I found the 1851 census details of my great-great grandfather Charles Shields, immigrant from Donegal, living at 51 Main Street, Gorbals. There is a long list of people at this address, some living in the main building and others in what are described as the "backlands". There is a third entry under "wooden shed", and that is where I found Charles, his wife, Bridget, and five children. A family of seven living in a shed. How's that for street cred in the Monty Python we-were-so-poor stakes?

This first Charles was a labourer in an ironworks, possibly the Dixon Blazes just south of Gorbals. He died aged 54 from chronic bronchitis. Charles had managed to get the family out of the shed and into a house in Buchan Street. His final gift to wife Bridget was a daughter, Grace, born the year he died.

Although sad to think of them living in a shed, I was delighted to find Charles and Bridget with their brood: Susan, Mary, John, my great-grandfather Charles, Daniel and wee Grace. Growing up, I had a big immediate family of three brothers and three sisters but since both my parents were only children there was a distinct lack of uncles, aunties, and cousins. I have discovered a satisfyingly vast cast of relatives. There are multitudes of Prestons, McFadyens, MacArthurs, Mulhollands, Donegans, Cardles, Cassidys, Cavanaghs, Boyles, Diamonds, McDonalds and even some Campbells. I have not yet encountered any other branches of the Shields offspring of John or Daniel from that shed. My direct line is Ferdinand Shields of Donegal who begat Charles of Gorbals who begat Charles the coal miner who begat John who died in the First World War who begat my father Charles.

The Shields lived for almost 100 years in Gorbals, with my grandparents having a brief sojourn in Dundee. In 1940, my father, mother Annie, and their then four children left a crowded single-end in Camden Street to migrate to rural Pollok for fresh air and a three-bedroomed house with a bath to keep the coal in.

The early Shields were fodder for the industrial revolution: miners and labourers, although grandfather John found a trade as a riveter in the shipyards. The women worked mostly in mills and textile factories. One was a "hair beater", presumably making horse-hair mattresses. Theirs were lives relatively ordinary (if you don't mention the First World War), except for the second Charles, known for some reason as Painted Charlie, who went off the radar and maybe a wee bit off the rails. He could not be found in the 1871 census but reappears in 1881 married to Isabella Cassidy. He has subtracted seven years from his age.

Isabella died in 1890 in her early thirties, having given birth to my grandfather John and a daughter, Elizabeth. In the 1891 census, Charlie is living with his two young children and a much older daughter, Mary, herself married with a young family. Mary's 1866 birth certificate shows her mother was Agnes Johnston, "wife of James Cairns, coal miner". Charlie was also a coal miner, but perhaps on a different shift from Mr Cairns. Mary's mother appears on a subsequent record as Agnes Shields. The extent and nature of Charlie's relationship remains a mystery. The birth of my great auntie Mary is one of the more intriguing examples of family illegitimacy, which seemed to be a big deal in those times.

I remember confusion over my mother's maiden name, which I needed to fill in a school form. She told me it was Miller or MacArthur. Her mother, Annie McFadyen, my Wee Granny, married John Miller in 1902. But in the 1911 census she has a boarder called Archie MacArthur and in 1912 my mother is born. Archie is the father and the Wee Granny is listed as "wife of John Miller", as she was on her death certificate in 1940.

This has melodramatic Edwardian overtones of living in sin. But it was actually a love story. I'm told my Wee Granda Archie was one of the nicest men you could meet.

What happened to John Miller? We know that his father was a confectioner. Could we have been related to the Millers' pan drop dynasty? I thought so for at least an hour until diligent cross-checking revealed that our Millers had a shop in Maryhill.

I am happy with my Irish roots. I was chuffed to find out my mother was 100% Glasgow Hebridean with grandparents from four islands, which makes me Irish-Hebridean, a rich mixture.

I left the computer behind to visit some islands, using my bus pass to get to the beautiful village of Portnahaven on southwest Islay where the McFadyens worked as fishermen. I walked the fields of Claddagh where they were cottars (crofters who don't own their land) until the mid-1800s when human beings were replaced by more profitable sheep. Great-grandfather Alexander came to work in a Glasgow distillery, a job befitting an Islay man.

On Islay I met an impressive lady called Betsy West who, aged 99, is sharper than a tack and was able to fill me in on the McFadyens. Betsy is also descended from my great-great grandfather Finlay, the fisherman, and I am honoured to call her cousin, if somewhat removed.

In the Museum of Islay Life, I found the story of the ship Mary Anne, which in 1859 ran aground with a cargo of whisky. A contemporary report states: "The police, Sergeant Kennedy and Corporal Chisholm did their best to prevent looting but to no avail. Donald McFadyen, a Portnahaven fisherman, died on the rocks from the drink." Donald, the whisky on the rocks man, sounds like one of my relatives.

My pilgrimage took me to Ellenabeich at Easdale, home of my great-grandmother Ann Campbell. Set in some of Argyll's most striking scenery, it is scarred from its time as a centre of the slate industry.

The Slate Islands Heritage Trust visitor centre has the whole story of Ellenabeich. Ann's father Archie Campbell's life in the 1840s as a slate quarrier would have been one of hard toil and daily danger from precarious rock-climbs to errant explosions. Quarriers were paid by the landowner proprietors only after the slates were sold. Most of the year was spent in hock to the company store. Archie Campbell died in his thirties, either through accident or working in atrocious conditions. His wife Janet was left with six children under 15. Ann would have been working, carrying baskets of slate waste at an early age.

I have travelled through North Uist many times but did not realise I had roots there. My great-grandmother Johanna McDonald's family (also cottars) lived in Baleloch. Johanna's grandfather George's occupation is listed as piper. You cannot get more Scottish than that. Unless, of course, he was some sort of plumber and not a bagpipe player.

The last of my mother's Hebridean homes is Tiree where the Wee Granda hailed from. Like the Islay McFadyens, the MacArthurs of Balinoe were fishermen, crofters and sailors. I constructed a detailed picture of the MacArthurs through parish records which have been diligently put online by local volunteers. An Iodhlann, the Tiree historical centre, is a valuable resource. Life on Tiree was not without its rigours, including a potato famine in the mid-1800s and biting cold due to the scant supply of peat and firewood. My great-great-grandfather John managed to live to age 90.

Great-grandfather Neil became a merchant seaman based in Port Glasgow, which may explain my fondness for the tales of Para Handy. Then he came to live in Glasgow to work in a distillery.

There is a tragic moment in the history of the Tiree MacArthurs. Great-uncle Archie's entry ends: "Died in the fishing banks off Skerryvore lighthouse, April 30, 1858." He was one of four fishermen who perished when their small open boat was swamped by heavy seas in a sudden gale. John MacArthur was watching from the shore at Hynish the desperate efforts of his son and fellow crew members to reach land. He told the subsequent accident inquiry: "They were making no progress as the wind and the tide were against them and a very deep sea on. I was looking at them until dusk when I lost sight of them."

The Hebridean blood in my veins must have contributed to my fascination for the islands and the many trips made before I knew there was any family connection. The Presbyterian ancestry is probably why I have long considered myself a Roman Calvinist. I regret not having the Gaelic which my island ancestors undoubtedly spoke, and the Irish Gaelic of my Donegal forefathers. I suppose that makes me a bit of an Erse.

I think back often to Bridget McDade, the mother in that wooden shed, who must have been a brave matriarch. Widowed with six children she became a "dealer in fish": the first of many women in the extended family to be a fishmonger, while the men up in the islands were fishermen. Bridget had a lingering death from lip cancer. Like a depressingly large number of my relatives, she passed away in the Govan Poorhouse, the forerunner of the Southern General Hospital.

It turns out I did have an auntie. My mother had a twin sister Johanna, who died aged six of measles and broncho-pneumonia in 1918. Mother never told me about Johanna.

Who do I think I am? Someone who is proud of and inspired by the endurance and fortitude of his family through the ages. Genealogy can be life-changing.