As a child, Sir Patrick Stewart learned to love the songs of Irish tenors. If his father, Alf, came home singing "The Mountains of Mourne" or his favourite, "I'll take you home again, Kathleen", then his mother, Gladys, was safe. The actor, now 72, and his older brother, Trevor, lived in terror of military tunes. "We would lie awake in what was really no more than a partitioned-off corner of my parents' bedroom, waiting for him to come back. Nobody went to sleep. We would listen as he came into the yard. If he was singing army songs, that was bad news. Then he would find fault with something and then the conflict would escalate.
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"Calling the police was not an easy thing to do in the 1940s, so someone had to go to the phone box, which was at least 500 yards from our front door, and make a 999 call. Often the call was not made." When it was, the police would come, the ambulance service and doctor would come to the family home in Mirfield, West Yorkshire. "My mother would be lying on the floor, bleeding," says Stewart.
"The kinds of things said were unbelievable. A policeman once said, 'it takes two to make an argument', or, 'well, she must have done something to upset him'. Which is a way of saying he must have been justified to be violent, and we know there is no justification for being violent. None whatsoever."
Often Stewart was forced to step in to defend his mother from his father's explosive rage. "I became an expert at judging the heat of an argument," he says. "As the temperature rose I would get out of bed and on to the landing, and, if it rose further, I would go down the stairs, sitting on the stone steps so as to be as close as possible to the door if something bad happened. If the escalation continued I could try to intervene.
"Now, it is really sad when a child becomes an expert on those kind of issues. But I was and I knew exactly the moment when I would throw the door open and rush in and say 'Stop!' or literally put my body between them."
Stewart's life now is a world away from his childhood horrors. After working for years on the stage and in television roles, in 1987 he moved to Hollywood and spent seven years playing Jean-Luc Picard in the science fiction series Star Trek: The Next Generation. In 2004 he returned to Britain to focus on the stage.
I am speaking to Stewart in the swanky offices of a business donor who has bid to have lunch with the actor to raise funds for the domestic violence charity Refuge. It is the one The Independent on Sunday has chosen for this year's Christmas appeal. "The work I do with and for Refuge is for my mother, because I could not do it for her then," Stewart says. "She had nowhere to go and Refuge, had it existed, would have given her an option or choice."
In the family's cramped, one-up one-down house there were no choices and no escape. At times the neighbours had to step in. "On Monday morning, the walk to school was so difficult, because I knew everyone had heard and I was ashamed and embarrassed. Lizzie Dixon was our next-door neighbour, a physically impressive woman. There were times when things were bad and the door would burst open and Lizzie Dixon would march in and she would thrust her great forearm in my father's face and say 'Come on, Alf, try it on me!'"
Stewart has tried to understand what led his father to become so violent. He thinks he suffered shell-shock. The nosedive his dad's career took after the Second World War made everything worse. "He had come out of the army as a superstar, a regimental sergeant major [going] to unskilled work and labour when he had commanded a battalion and the day-to-day respect of his colonel."
Though he could be an ogre on Friday nights, Stewart senior had another side. His son recalls: "He was very charismatic. Later on, in the theatre, I had to keep an eye on him whenever I took him backstage, because he would take actresses into corners and they would say 'your father is such a wonderful man' and yes, he was. But coming home from the pub or the club, behind closed doors, he was an angry, disappointed, violent man."
Acting helped Stewart to escape the traumas at home. "When I was 12 an English teacher, a man who made everything in my life possible, Cecil Dormand, put me in a play. "The first time that I walked on stage in my school dining hall I felt safer than I had ever felt in my life. Looking back, the reason I was always so comfortable on stage – the reason I have never had stage fright in my life – is because the stage is where I live. That is my home, or in front of a camera. It is my refuge."
There are few signs of Stewart's past in the man sitting in front of me. There is no trace of Yorkshire in his voice: his accent is more Received Pronunciation than the Queen's. And he holds himself with a composure and confidence that belies his early traumas.
After spending most of his life looking older than he was – he went bald when he was 19 – he now looks much younger than his 72 years. Dressed in a pressed shirt and trousers, capped off with a leather jacket and a trendy skinny tie, it is the garb of someone a quarter of his age, but he somehow pulls it off.
He has just finished filming a documentary about the racing driver Sir Stirling Moss. Racing Legend will be aired on BBC2 in Christmas week.
Stewart shows boyish excitement about the project, which he presents. "I am very proud of it," he says, "if for no other reason than because I get to drive some incredible cars.
"I learnt to practise drifting at Caterham. Then I drove a 1953 Vanwall, the car that Stirling won the British Grand Prix in, which is a monster, a brute. Stirling would not drive it. I asked him to drive it and he said 'no, no, no: you are not getting me back in that'. Most excitingly I drove a 1956 Mercedes Gullwing on the Mille Miglia course with Stirling as a passenger, talking me through when he won at the Mille Miglia, which is a 1,000km race without any stops. The biggest compliment in my life I have ever been paid is that he fell asleep while I was driving."
His passion for cars is a long-standing one, though the racing part is recent. "All my life [I have loved them]. It is ironic, given that my parents never owned a car. Cars were totally remote in my life, except that on the corner of my street there was a family that had a little hairdressing business called Maison Sheila, and the husband had some other private business somewhere, so they had a bit of money. He had a 1937 SS Jaguar. He also had a daughter called Valerie who sadly died a week ago. Valerie and I used to hang out in the back seat of the SS Jaguar and I have always said that that is where my love for Jaguar cars came from, and for fine motor engineering.
"When I was living in California I got involved in motor racing and I enjoyed it. This year, at the age of 72, I actually got my racing driver's licence. The only problem with my racing driving is that I do not like speed much, and that is a handicap. I do not like going incredibly fast. I like going fast, but not to the point where I no longer feel safe. I love the technique of racing driving."
The day after the interview, Stewart was due to jet off on another project, this time in New York. He is starting rehearsals for a new film called Match about a classical ballet teacher.
But don't expect him to be abandoning the British stage altogether. "I came back to the UK after 17 years because I was dissatisfied with the work. I worked all the time, but it was not the work I wanted to do. I wanted to go back to my previous life, pre-Star Trek, which was classical British theatre, the Royal Shakespeare Company, the West End. That is what I have done for eight years and they have been the best eight years of my life."
The Independent on Sunday Christmas Appeal is for the national domestic violence charity Refuge. To make a donation visit: http://refuge.org.uk/independent-on-sunday-appeal/