Having found international fame as Samantha in Sex And The City, actress Kim Cattrall has become forever associated with Manhattan. In fact, she was born in Britain, but raised in Canada. “Whenever I think about family, I think about Liverpool,” she says at the start of her episode Who Do You Think You Are?

At the centre of her family’s story lies a mystery. Seventy years ago, Kim’s grandfather, George Baugh, walked out on his wife and three daughters. Kim’s mother, Shane, was just eight years old and remembers her father trying to persuade her to leave too. Nobody in Kim’s family ever learned what happened to George. “I think it’s going to end in tears,” says Kim as she heads for a meeting in Liverpool with her mother and her two aunts, Marjorie and Dorothy.

The trio’s tales of life in inner city Toxteth after George abandoned them are harrowing. Liverpool in the 1930s was a city where around 15 per cent of the population lived below the poverty line. Kim’s grandmother had to sell everything to keep going. There was no furniture, they drank from jam jars, the three girls shared a bed. The sisters don’t even possess a picture of their father, beyond one where he can just be glimpsed peering from behind a curtain.

One possible clue to his whereabouts is an old newspaper cutting from 1980. It’s the story of a wedding dress handed down through generations of the Baughs. Using the cutting as a starting point, Kim is able to track down two of George’s sisters, Edna and Amy. George, Kim learns, disappeared from their lives too. A picture emerges of a man who was son of an alcoholic and constantly ran away from home. George’s sisters think he may have emigrated to the USA.

There’s a grain of truth here. Checking passenger records, Kim’s amazed to learn that George was a stowaway on a ship to New York in 1935, but was sent home.

“I’m piecing together a picture of a man who doesn’t have a tremendous amount of responsibility,” says Kim, “except to his own desire and needs, he’s quite selfish.”

There’s a bigger shock ahead. Marriage records reveals that George was a bigamist. On 5 August 1939, the year after he abandoned his first family, George married 21-year-old Isabella Oliver.

Kim’s next stop is Durham. At the county record office, she learns that George had at least three children with Isabella. She also finds an address for George on an old electoral register: in the village of Tudhoe.

A phone call later and she meets Isabella’s sister-in-law, who used to live next door to George. She had no idea George was a bigamist. For the first time, Kim sees old photographs of her grandfather. A photograph of a happy-looking George at the beach is especially hard for Kim to view. “He’s just living right in the moment and is not looking back, has no regrets, no sorrow,” she says.

In 1961, as a so-called ‘Ten Pound Pom’, George took his wife and four children (another daughter didn’t show up in Durham records because she was born in Manchester) to Australia and never returned home, another selfish decision because Isabella didn’t want to go. He died in 1974 in Sydney. Isabella lived on until 1990.

In Canada, Kim gathers her mother and aunts together and tells them what she’s learnt. It’s a hugely emotional meeting. “This moment of finding him was really more about finding the family that I do have,” says Kim, “and that’s a great gift.”

And perhaps about finding a new family too: Shane, Marjorie and Dorothy are now in touch with their Australian relatives.