There are some virtues to going bald early. At the age of 18, Sir Patrick Stewart (as he then wasn't) lost all his hair as a result of alopecia. The ravages of time have not worked conspicuously on the unchanging dome. Stewart looks eerily similar now to the man who played, nearly 30 years ago, Jean-Luc Picard in Star Trek: The Next Generation or, a decade before that, Sejanus in I, Claudius.

Just look at Stewart scowling as the steely neo-Nazi in this week's superb Green Room. Now 75, the years have barely withered him. That rich Shakespearean voice shows equally little evidence of passing decades.

"The reviews for Green Room were wonderful," he flutes. "I was mostly happy with what they said about me. One did, however, say that it was a shame Patrick Stewart was so 'theatrical'. 'Why couldn't he match the naturalism of the younger actors?' I laughed at that. Darcy Banker is the most untheatrical performance I've ever given. Look, I know I'm known for screaming and shouting. Ha ha."

Darcy Banker, a precise character with a chromium stare, leads a gang of rural fascists who besiege a punk band led by Anton Yelchin and Imogen Poots. Like so many totalitarian demagogues, Banker mixes unmistakable charisma in with his lunacy.

“Yes, they do that, don’t they?” Stewart says. “You have only to look at that footage of Mussolini. I have always been able to understand why there was an appeal there. It would never have appealed to me, but I understand that. I made sure [Banker] was as warm and friendly as possible.”

Stewart says he is known for “screaming and shouting”, but that’s not really fair. There are Shakespearian actors about whom one might make that accusation (his lifelong friend Brian Blessed, for one), but Stewart’s trademark has always been that mellifluous, old-school voice. If you didn’t know he was brought up in a working-class corner of Huddersfield, you would be unlikely to guess. Scarcely a trace of Yorkshire remains in his vowels.

“I didn’t just have an accent. I spoke Yorkshire dialect,” he says. “If I was going to a friend’s house I’d say: ‘Is thoo cumin’ oot tee lark?’ That is: ‘Are you coming out to play?’ It’s dialect.

“But I had an acting teacher from the age of 12 who taught me received pronunciation. A number of others – including Brian Blessed, incidentally – also attended that class. Very early on in my acting lessons, she said I would need to learn to speak ‘properly’. At her house I’d speak standard English. During the week I’d speak broad Yorkshire. I had to be careful not to mix it up. I’d be hit over the head if I spoke upper class with my friends.”

I wonder if he ever slips back into it. “Oh, yes. When I am on the phone to my brother, my wife says that I almost immediately become incomprehensible.”

True north

As Stewart explains, the irony of all this was that while he was learning to speak like a southerner, actors such as Albert Finney and Tom Courtenay were spreading their northern intonations about the London stage. Had he held on to his Yorkshire accent, it might have proved a selling point.

Nonetheless, Stewart did reasonably well, reasonably quickly. Beginning in Lincoln, he worked his way up the repertory theatre ladder – stints in Sheffield, Manchester and Liverpool – before winding up at the Bristol Old Vic. That led to an audition for the Royal Shakespeare Company.

“I had no ambitions or dreams to become a film or television actor,” he says. “My dreams came true when I got to the Royal Shakespeare Company. I had worked for that systematically since I left school in 1959. I finally joined the RSC in 1966. I had really worked my way through the ranks.”

He still retains a razor-sharp memory of the audition with Peter Hall (on a "rainy Sunday evening") that brought him to the RSC at Stratford upon Avon. Fourteen years of superior work followed. Stewart starred alongside Frances de la Tour and Ben Kingsley in Peter Brook's legendary production of A Midsummer Night's Dream.

Stewart shows up in John Boorman's Excalibur and, on television, despite not speaking a word, was unforgettable as Karla, George Smiley's arch enemy, in the BBC adaptations of Tinker Tailor Soldier Spy and Smiley's People. But he wasn't any sort of star until Star Trek: The Next Generation came along. Oddly, it all happened as a result of a lecture at UCLA.

"It was an extraordinary fluke they'd heard of me," he says. "A friend of mine, who was a Shakespeare scholar, asked me to do readings to illustrate a lecture. Robert Justman, one of the producers on Star Trek, was signed up for the lectures.

"The next morning I got a call from my agent in Los Angeles – who I'd never even met, because I'd no interest in working there – and he said: 'Can you tell me why the producers of Star Trek would want to see you, and what the hell were you doing at UCLA?'"

The same afternoon, he found himself with Gene Roddenberry, creator of Star Trek, who, after he'd left, told Justman that the meeting was a "total waste of time".

“I am told there was a memo that then went round saying: ‘I do not want to hear Patrick Stewart’s name again’.”

Nonetheless, Stewart got the job and the series, the first live-action TV incarnation of Star Trek in 20 years, became a sensation. It was inspired casting. Stewart had the same swagger as William Shatner, but the wit and levity to his delivery added new flavours.

Don’t do it

“I was befuddled by it all and in complete denial for some time,” he says. “Everyone I knew said it would be a failure. ‘Don’t worry about signing that six-year contract. It won’t get through the first season,’ they said. I remember Ian McKellen saying: ‘Don’t do it.’ More people watched the first episode alone than had ever watched me in every play I had ever been in.”

It's interesting that McKellen comes into the conversation at this point. As it happened, both northern Shakespeare specialists managed to move from success in popular sensations to unofficial pension plans in the X-Men films. McKellen is the older Magneto. Stewart is the senior Prof Xavier. They have also shared the stage in two notable recent productions: Samuel Beckett's Waiting for Godot and Harold Pinter's No Man's Land.

Meanwhile, Stewart has negotiated a colourful personal life. In 2013 – with McKellen performing the ceremony – he married the singer-songwriter Sunny Ozell. At 37, she is a full 38 years his junior. This is his third marriage. “I must bring my wife to Dublin,” he booms. “She has just about everything European in her heritage. I think there is some Irish. I know there is some Danish and she has some Russian. She is also Native American.”

Where do they spend their time? He seems busier than ever.

“We live in Brooklyn and in London and West Oxfordshire. When we don’t have to be anywhere for work it’s Oxfordshire. Thanks to streaming and podcasts, I can have the BBC in my ear at all times. I listen to match-day commentary of my team on Radio Leeds. All of which is great.”

What a funny thing to happen to a wee boy from the West Riding.