John Hurt’s sense of himself has always been wrapped around a family myth and to prove – or disprove – its truth he agreed to take part in the genealogical TV series Who Do You Think You Are? Like many of the celebrities who have agreed to a televised trawl through their family history, Hurt was in for a surprise.

The resulting film is a detective yarn, a surprising psychological study of one of our greatest actors – star of The Naked Civil Servant and The Elephant Man – and a reminder, if one needed it, of how much sway class still holds over the British, even though we are supposedly all middle-class now.

In search of clues to his ancestry, Hurt traipses from splendid Irish monasteries and aristocratic Irish castles, through dour, middle-class Grimsby, where he spent his teens, to an Ann Summers sex shop in Croydon which in the 1850s was “Miss Thompson’s Establishment for Young Ladies”. There his great-grandmother Emma Stafford, who might hold the key to the enigmatic truth about Hurt’s class roots, was schooled and became a governess.

“Family legend has it that my great-grandmother was an illegitimate daughter of an Irish lord,” says Hurt. He always believed this “deeply beguiling” myth that Stafford was the illegitimate daughter of the Marquis of Sligo, meaning that he had both aristocratic and Irish origins. And, when you think about it, it’s a myth that you can hear clear as a bell in Hurt’s accent. It betrays nothing of stolid, middle-class Grimsby, or the Derbyshire coalfield village in which he was born, but rather suggests that he must surely hail from some raffish aristocratic Anglo-Irish family.

Hurt’s immediate family was, in reality, neither grand nor rich. He, his older brother Michael, who is now a Benedictine monk at a monastery in Ireland, and their adopted sister Monica (who died recently), were the children of a Church of England vicar of rigid beliefs and puritanical tastes.

“He hated materialism and lived like a pauper all his life,” says Hurt. “His stipend was ridiculous, about £500 a year. All he spent on himself was the newspapers and an ounce of tobacco. He had one suit which he wore until it fell to bits, one cassock which he wore until it fell to bits.”

Until Hurt was about 12, his father worked in the mining communities of Derbyshire. Yet the family had aspirations. As the child of a clergyman, even one so poor, from the age of eight Hurt was packed off to boarding schools in the south of England.

The Hurts were one of the few middle-class families in the area, so his natural playmates would have been the miners’ children.

“There is always an irony in life,” he says. “I wasn’t allowed to play with them because they were ‘common’. That’s my mother, who was working class or maybe lower middle class. She had a very northern posh accent and of Khrushchev she would say, ‘Oh, you wouldn’t want him to be head of your government, would you. He’s got nothing aristocratic about him at all’. No, that’s the purpose, Ma. That’s what the Russian Revolution was about!”

I wonder if Hurt’s mother had latched onto the story about Emma Stafford, her husband’s grandmother, having been the illegitimate daughter of the Marquis of Sligo as a way of gaining some kind of class leverage.

“She would have liked that, yes,” says Hurt, although he says he can’t remember if she knew the story. “She liked to have a grand side to her. And I love that way of life. I love it all. I adore the architecture, that sort of scope.”

He had hoped, given that his grandmother’s family name was Browne, to discover whether he might be “some sort of distant 15th cousin to Garech Browne”, also known as Garech de Brun, one of Hurt’s oldest friends and a man he evidently holds in the highest esteem.

Garech Browne, son of the 4th Lord Oranmore and Oonagh Guin-ness, has been a charismatic figure in bohemian circles for the past half-century; he is an important patron of the arts and, by founding Claddagh Records, has been a significant supporter of Irish music. When in Ireland he lives at the enormous Luggala Estate just outside Dublin.

However, the search for Hurt’s roots seems to show he is neither of noble lineage nor Irish.

“I am not who I believed I was,” he says forlornly at one point. “That really upsets me.”

The mystery around his great-grandmother’s parentage seems to have come about because she was a ward of court. There is an interesting story around her parentage, but it’s not the one he thought he would find. The film makes much of his disappointment, although Hurt remarks acidly that he believes it has been edited to make him look “a prick”, obsessed by class, desperate to prove that he really comes from aristocratic Irish stock, not from the solidly lower middle-class English family in which he was brought up.

At the large Spanish-style house in the Hollywood Hills where we meet – which has been rented for him and Anwen, his fourth wife, while he shoots the latest instalment of the Indiana Jones saga for Steven Spiel-berg – he insists that it is not the lack of a noble link that upsets him, but finding that he’s not Irish.

That belief was “one of the bankers in my life”, he says. “As far as I was concerned I was Irish. My disappointment was that they had managed to prove that the one thing I thought I did have was Irish blood and I haven’t got any.”

Hurt has always felt so deep a connection with Ireland that he lived there for many years, only returning to England about five years ago. And his behaviour sometimes seemed to put him neatly into the box marked “Irish hellraiser”.

“Oh, I don’t think I was,” he replies, seemingly put out that anyone could possibly think such a thing. “I got caught a couple of times being pissed in public by the press but I wasn’t an O’Toole or a Harris. I don’t drink at all now.”

Hurt also maintains that he has a far more bohemian view of class than this journey through his background might suggest. He says that is partly why he became an actor and why he felt so at home in the artistic world when he arrived in London in 1960, just 20, to study first at St Martin’s, then at Rada.

There, particularly in Soho, he found he could escape the constrictions of his middle-class background. “Awful generation; they had no freedom emotionally,” he says. “I was intrigued with artists and those sort of people. That’s where I found everything the church promised: kindness and interest and feeling, whereas the church was frigid, dogmatic, rigid, unfriendly.”

I wonder if, to escape from the small-minded cold world of the Grimsby vicarage, Hurt had somehow found it necessary to throw around himself the mantle of secret Irish aristocracy – and if he feels differently about himself now that he has discovered the truth?

“The point is one has lived too much of oneself to feel different,” he says. “Now I’m old enough to be able to say I am who I am anyway. It doesn’t make much difference.”

But I’m not so sure . . .

Who Do You Think You Are? will be broadcast on BBC1 at 9pm on Thursday

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