Who Do You Think You Are? - Sarah Millican, BBC One

It's a testament to how good an idea Who Do You Think You Are? is that well into its tenth series (and several others worldwide) it still provides great entertainment – and not a little emotion. Its secret, I suspect, lies in the fact that every family has its stories and dramas and last night's subject, comic Sarah Millican, uncovered some interesting tales buried several generations back, long lost from current family folklore.

The comedian is, by her own description, a home bird (the title of her latest tour), deeply rooted in her working-class South Shields origins – so much so that she has a collection of Geordie music, including, she said without a trace of embarrassment or irony, Robson & Jerome, which she plays whenever she drives home to visit her parents, former hairdresser Valerie and ex-miner Philip. She wanted, she told us at the top of the programme, to find that her family's connections to the area go back several centuries; her parents, meanwhile, spoke of the possibility of a rich relative and Scottish forebears, and their hankering for a bit of adventure in the family line.

At first her search uncovered several male antecedents doing “Geordie bloke jobs” such as fitters and stokers, but then, to her genuine amazement, a great-great-great-grandfather was listed as a diver, and from Kent to boot. A southerner in the family was a discovery indeed – but a diver, in the early 1800s?

He was a salvage diver, and a pioneer of the profession. Millican was sporting enough to dress in the rudimentary garb of the time – making her look like she was about to take part in a sumo wrestling match, albeit with leaden boots and a metal helmet – provided by a museum in Whitstable, where he plied his trade.

But it was when a historian delved deeper and found press records of his derring-do – salvaging from the Pegasus, a sunken passenger ferry in which 55 people died – that it took an emotional turn. Millican was clearly struck by the thought that he had made money from others' distress, but it turned out that he had dived, at great danger to himself, not only to bring bodies back for burial, but to rescue precious goods of victims to give to children orphaned in the disaster.

Not for the first time, Millican was moved to tears. And when the hunt started on her father's side, another heartbreaking story emerged. Her great-great-great-great-grandfather was an Orcadian who had worked as a general labourer for the Hudson's Bay Company in Canada and had suffered severe frostbite, resulting in his feet being amputated.

Disability is a subject close to Millican's heart (although this wasn't explicitly addressed in the programme), and the tears came again at the thought that he may have been cast aside, but remarkably the company found him work he could do sitting down. Sometimes our view of history, cruel and heartless though much of it was, is changed by glimpses like this.

Unusually for many migrants at the time, her relative had returned to the UK and, while not exactly prospering financially, married and had children, for which British comedy should be duly thankful. It was important to Millican that she be proud of her family, however far back they were - as she said of one of them: “It's what you want in an ancestor – essentially a good man.” Quite so.