Who Do You Think You Are? (BBC1) is now approaching something like its 900th series so it was a pleasant surprise to find tonight's subject was Billy Connolly.

Other celebrities in this series have included Reggie Yates, Brendan O'Carroll and a former Eastenders blonde so you'd be forgiven for thinking barrels are being, if not scraped, at least sternly prodded. Yet, they've managed to provide the Big Yin whom the narrator tells us is 'the wild man of comedy and an international star.'

There's an emphasis, then, on stardom but a programme about a person's family history shouldn't be concerned with big celebrity names but simply about featuring a good story. There's no point showcasing Brad Pitt if his ancestors were a bunch of straitlaced librarians. The programme makers should be opting for the guest with the racy or tragic past, even if that does mean having Mavis from Coronation Street instead of a Hollywood hunk. They are surely hunting out big stories, not big celebrities, so does it matter which starry name is appended to this programme?

Yes, because this is BBC1 prime time, so the viewers are in it for the celebrity, and rightly so. If the programme was truly about genealogy and social history then it would be tucked away on BBC4. This programme is about celebrity and so it needs a star name to prop it up.

But tonight we needn't have worried that they're running out of famous subjects. This episode gave us both a big name and a big story and it was a pleasure to watch.

The programme opened on Billy Connolly's magnificent Highland estate and we were allowed into the castle. As he sat at his kitchen table scrutinising old census forms the programme felt more like Through The Keyhole but with calligraphy thrown in. I'm not ashamed to say I was more interested in gawping at the castle and decor than in listening to the narrative. Who lives in a house like this?

When I finally snapped to attention it was to hear the Big Yin say he's 71 now, so is getting closer to death. This has turned his thoughts towards learning about where he came from. He said he's also keen to uncover a mad, maverick ancestor so he can shout, 'that's the one! That's where my DNA came from!'

Billy Connolly's family history began as you'd expect: lots of black and white photos of cheeky weans playing in the streets of Anderston, coupled with praise for the strong women who helped raise him: all typical Glasgow working class tropes. In fact, things were so strongly flavoured with Glasgow that, at one point, he squinted at the faded copperplate on a census form and asked if his ancestors had indeed lived at what appeared to be '40 Daft Street'.

His family tree started with O'Briens and Doyles and we learned they were poor Irish immigrants. Not wishing to sound cynical this is a story we've all heard before. So many of us, particularly in Glasgow, are descended from Irish immigrants so I settled back expecting to hear familiar tales of poverty and courage and hard labour in the mills and factories - good stories, but ones I've heard so often. My maternal family are the Boyles and now here was the Big Yin with the Doyles.

But here the programme veered off course spectacularly. They couldn't trace a baptism certificate for his Gran in either Scotland or Ireland - and that was because she was born in Bangalore. This woman Billy only ever knew in the damp, cobbled streets of Anderston had actually been born in a far-flung exotic land.

So off he went to India, and was soon on a rickety bus racing past lush tea plantations and springing monkeys. So much for the elite discourse of the weary lumpenproletariat living out their dreary lives in the same ramshackle street. Billy's ancestors were charging all over the globe and that is how he found himself at the splendid Wellington Barracks in Bangalore where his ancestor, Daniel Doyle, was a flashy member of the Royal Horse Artillery. However, old Doyle was a bit too flash for his own good and was soon demoted for various 'defaults'. He also drank heavily and dallied with prostitutes and was repeatedly admitted to hospital for a list of troubling things, including diarrhoea, excessive urination and syphilis.

The Big Yin was able to laugh at this, saying Doyle was 'an incontinent alcoholic and mad shagger!' which proves he's a chip off the old block.

This programme showed we shouldn't think of our working class ancestors as always being downtrodden victims, huddled in doorways with pinched faces and bare feet. As the Big Yin reminded us, some were rambling across the globe, some were adventurous, some were cruel, some were brave and I suppose some were just 'mad shaggers'. It's comforting to know some things never change.