LS Lowry was convinced his paintings would be worthless after his death, he confided in a previously unheard interview.

Although the artist had enjoyed some success in his final years, Lowry could never have imagined he would become one of Britain’s best-loved artists or that his paintings would sell for millions of pounds.

Going to the Match, his 1953 painting of crowds of spectators streaming into a football stadium, sold for £7.8m in 2022.

Half a century after his death, he is now being portrayed by Sir Ian McKellen in a BBC documentary, LS Lowry: The Unheard Tapes, which draws on a trove of previously unheard audio recordings.

Described as “the last words of a great artist” who was an intensely private man, McKellen will lip-sync his dialogue.

In the tapes, the artist is heard to say: “Some day, you may be walking down some street and look into a junk shop window. You’ll see a picture upside down, marked cheap, 30 shillings. And it’ll be mine.”

From 1972, over a period of four years, Lowry gave his longest, most revealing interview to a young fan, Angela Barratt. She died in 2022 and the tapes remained hidden in her Manchester home. They have never been broadcast until now.

Lowry bared his soul to her. He confided that his family and friends had teased him about his paintings. “I made no money,” he said. “People laughed heartily at them … All my friends used to joke about it: ‘How’s the art trade?’; ‘Are you making your fortune out of it?’; ‘Don’t be such a fool, why don’t you give it up?’”

Lowry had enrolled at the age of 17 for evening art classes. On selling his first painting, he said: “It was in 1921. And I got the sum of £5 for it. I was 34 … My family got the shock of their lives when I sold it. They couldn’t believe it was possible I could sell anything.”

Asked whether his mother liked his paintings, Lowry replied: “No, I don’t think so. And me father [who worked as a clerk for an estate agent] used to have hysterics if I sold a picture. He couldn’t understand it.”

Lowry became disheartened: “I was often very, very fed up. I said what’s the point of doing this, many a time.”

Yet Lowry is loved by the public for his unique depictions of working-class urban life, mill scenes and industrial landscapes in the north of England, peopled with his distinctive matchstick men.

When his family faced financial difficulties, they moved to Pendlebury in Salford, then an area blighted by pollution, noise and poverty: “I didn’t like it at all for a long time, and I couldn’t get used to it. And then I got fascinated by it. I began to think after a time, has anybody ever painted this scene? And I found they hadn’t.”

Asked whether he preferred an “industrial” view to “places which are beautiful”, he replied: “I don’t like the south of England, if that’s what you mean. It’s harmless. No guts in it … Dull … Horrible place.”

Lowry worked as a rent collector for the same Manchester property company for 42 years. He feared that if people knew about his day job they would assume that he only painted in his spare time and was therefore an amateur. He really wanted to be taken seriously.

One of his friends says in the documentary that they only found out about his job after he died. “Somebody told us, and in all honesty, we didn’t believe it. We thought that they were mistaken. It was a little hurtful that one felt that one was very close to this man, and he kept a secret.”

When Barratt paid tribute to him for putting the “industrial scene on the map [with] these wonderful paintings”, Lowry replied modestly: “That’s very nice of you. Thank you for that.”

He added: “I feel about my painting, I did as well as I could.”