Her mother should have known better. Even before she bought the piano to decorate the family home, the young Joan Armatrading had set her heart on becoming a musician. And almost five decades later she is still at it.

“I was born to write music; that’s why I’m here” she tells me while grabbing a few minutes’ rest before soundchecking for her concert at Leicester’s De Montfort Hall.

“When you are young you don’t think about things like that, but I knew I’d be playing until I died. And that hasn’t changed. The whole purpose of Joan Armatrading being on earth is to write. There’s nothing I can do about it.

“I didn’t wake up one morning and say ‘I want to write a song’. I woke up one morning and wrote a song.”

It is exactly 40 years since Caribbean-born Joan Armatrading MBE, 61, released her first of 17 studio albums, Whatever’s for Us. Since then, the Ivor Novello-winning songwriter has captured the hearts of millions, her bittersweet love songs providing the soundtrack to some of life’s great moments – times of joy and heartbreak. Best known for her smouldering 1976 hit Love and Affection and follow-up Show Some Emotion, she has not only enjoyed huge success as a solo artist, but has worked alongside members of Fairport Convention, the Police, and Bruce Springsteen’s E Street Band. And it is all because of that piano.

“I was young then, only 14, but I had been writing limericks and jokes when I was even younger,” she says.

“I started writing songs when mum bought the piano. She thought it was a great piece of furniture and knew which wall she wanted to put it against. She only got it because she thought it looked good; no one was going to play it.”

Fortunately it was in tune, and Joan wasted no time getting to grips with it, filling the family’s Birmingham home with music. “I’m self-taught in everything I do,” she says.

And that includes her first love – the guitar. Although her musician father had a guitar of his own, she was forbidden from playing it. So when she saw one in a pawn shop window she knew she had to have it.

“I was passing the pawn shop, saw the guitar and asked if I could have it,” she recalls. It was £3, but we didn’t have the money so my mum said I couldn’t have it. She did manage to swap it for two old prams though.

“I’ve still got it. I keep it on the wall; it’s got no strings though.”

Those stories about her childhood are as close as Joan gets to discussing her personal life. She is famously private, and has always shunned the celebrity lifestyle.

“I haven’t met a lot of people,” she says. “I am fairly private. You won’t see me in the gossip columns. Everything you’ve read about me is true... because you haven’t read anything!”

“I don’t hate the celebrity life, though. I think it’s fantastic and I love reading about it, it’s just not my thing. I don’t drink – I never have. In fact I’ve never even tasted alcohol – but that’s just me.”

So what does this disciplined artist, who has achieved success through her own hard work think of today’s breed of instant stars – the alumni of shows such as X Factor?

“I like them,” she says. “In fact I was watching X Factor just last night. People enjoy the experience of playing and I like that. For them it’s like going backpacking or on a big trek. It’s their once-in-a-lifetime experience – the first time they’ve played live in front of so many people. They know they’re not going to win but just enjoy the opportunity.”

So what is she most proud of? Her chart success? Her multiple awards and Grammy and Brit nominations? No.

“I am most proud of getting my BA Honours degree,” she says, referring to the history qualification she earned with the Open University, of which she is now a trustee.

“But I am also proud to write songs people are interested in.

“Pick a song like Love and Affection, which everyone knows; I wrote that in 1976 but it is regarded with more affection now than when I wrote it. People play it for great moments – to conceive and to give birth and for other milestones, good and bad. That shows people have a connection with it.

“The comedian Chris Rock says ‘the music you fall in love to becomes your music for life. The music he fell in love to was rap, which he still loves and always will. I know that’s what happens to my music too. It’s a great honour.”

Joan is part way through an epic 52-date tour, which reaches Oxford on November 18.

“I’ve been on tour since May,” she says. “I’ll take a break in December and then go back out until March.” Isn’t she exhausted? “Only by the travelling,” she laughs, complaining about the arduous trek south from Edinburgh, where she played the night before.

“Though once you start moving you get over it.

“I’m only going to places I like though. And I’m looking forward to coming to Oxford; I’ve been coming there for a long time now.”

The tour follows the release of Joan’s new album Starlight. The jazz-influenced record is the third instalment in a trilogy inspired by different forms of music. The previous two, Into the Blues and This Charming Life, being inspired by the blues, obviously, and rock.

Joan is under no illusion as to what people want to hear at her shows. But does she ever tire of playing her old hits? “The show is two hours long, and a song like Love and Affection is only five minutes,” she replies. “That says it all.

“I like singing those songs anyway. I wrote them all, remember. And Love and Affection is the song that got me known; I’d be crazy not to like it.”

Joan Armatrading plays the New Theatre on November 18. Tickets are £29.50 from atgtickets.com/oxford or by calling 0844 8713020