EastEnders hard man Ross Kemp tells of his sadness over the “dreadful” discovery his great uncle was a violent alcoholic who was blacklisted from British pubs – and never spoken about by his family.

For BBC1’s Who Do You Think You Are? the actor turned TV presenter finds that Albert Chalmers was brought up in a Portsmouth pub alongside his ten siblings, who included Ross’s great grandfather Arthur, nicknamed Pop. He imagines that the family might have had a ‘Disney-style’ existence, perhaps similar to his alter ego Grant Mitchell, who spent most of his time in The Queen Vic alongside his mother Peggy, played by the late Barbara Windsor.

But while Ross’s great grandfather Arthur was nicknamed Pop after Popeye, because of his successful life on the high seas, his great uncle Albert’s time in the navy didn’t end well after he was discharged.

Ross Kemp’s great uncle Albert was a violent alcoholic to threatened to cut his own mother’s head off

The actor discovers he spent years gathering court charges for being drunk and violent, with one report revealing he threatened to decapitate his own mother. Reading from the story in the local paper at the time, Ross says: “It was alleged he threatened to cut his mother’s head off, and everyone else in the house, at the same time chasing after her with a table k.n.i.f.e.”

Calling him “a bit of a wrong ‘un”, Ross learns that his behaviour not only led to several spells in prison, but also to him being barred from every pub in the land after he was named on the “blacklist” of the 1902 Licensing Act.

The 60-year-old dad of four says that the story relates to his long-running role in EastEnders. “It doesn’t matter whether I’m in Afghanistan or Columbia, I’m always going to be Grant Mitchell in a leather jacket going ‘get outta my pub!’

Ross’s parents, Jean and John, took the family all over Europe in the 1970s

“One story in the family, which I think has been very conveniently forgotten, is about Pop’s brother, my great uncle Albert, who was a bad man. A blacklister.” After learning more about his ancestor he ends up feeling some sympathy for Albert, who was sent to the Inebriate Reformatory for three years to try and cure his out-of-control drinking. The facility, contained within a prison in Warwick, aimed to reform inmates with no medical treatment other than denying them access to booze.

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It didn’t work and, just one year into his term in 1914, Albert was moved to a psychiatric hospital back in Portsmouth, at the age of 31. Ross, who has made award-winning documentaries, says the same problems are still commonplace today. “Having been to prisons in the UK recently, I see mental health issues and I see people with addiction issues. It’s dreadful to think that in four generations, very little has changed,” he says sadly.

Looking at a photograph of his troubled ancestor, he adds: “I feel very sorry for him. I look at the picture and think ‘there was a life there’. And he wasn’t remembered by anyone, even by his own brother. My great grandfather never mentioned him to his daughters and it was definitely not handed down to my mum and certainly wasn’t handed down to me.

Ross Kemp relaxes in Venice as a youngster with his mum Jean and brother Darren

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“Albert’s life was never really mentioned in the family history. This is not what I was expecting. I thought they all lived in the pub and it was all slightly Disney. The reality is my great uncle was an alcoholic with mental health issues and there is nothing romantic or sweet or sugar-coated about that.”

Ross says he can relate to both Pop, born in 1892, and older brother Albert, born a decade earlier, being in the Navy because he has always loved the sea. Brought up by his detective dad John and hairdresser mum Jean in Essex, Ross said that he and his brother Darren were taken on many trips around Europe in the early 1970s before it became popular. “We travelled at an early age when a lot of people weren’t doing that. I’ve always loved being in water. I strongly suspect that there is a connection to the ocean and to travel is in my DNA,” he says, before setting out on his journey of discovery.

In the programme he learns that his maternal great grandfather Pop transferred from the merchant navy to become an ordinary seaman at the start of WWI, quickly rising to become a quartermaster by the age of 22.

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Ross’s great grandfather Arthur ‘Pop’ Chalmers spent years working on the ships, missing valuable time with his family

When the actor wonders if there is any truth to the family story that he was later shipwrecked, he finds out that in 1943 Pop’s troop carrier, the Duchess of York, was bombed while en route to Algeria, 300 miles off the coast of Portugal. Dozens of men lost their lives when the ship sank, but Pop was one of the lucky ones, rescued and taken to the Allied-controlled port of Casablanca 700 miles away.

Ross, who is a qualified diver, becomes tearful as he imagines what his ancestor went through that day, saying: “I’ve been on my own in the water for a period of time and it’s frightening – you start to hallucinate. I’ve been lost at sea twice when I was diving – of course, it’s nothing like what Pop would have gone through, with the horrors of oil in the water, flames, and d.e.a.d men floating around you.”

– Who Do You Think You Are? with Ross Kemp airs on BBC1, 9pm,Tuesday 6 May