Spilling the beans on his excessive childhood was an unlikely move for successful portrait painter Alexander Newley.

But with memories of his famous parents Joan Collins and Anthony Newley, his overwhelming urge to recount his colourful, exuberant and often neglectful childhood proved overwhelming, and the title Unaccompanied Minor entirely fitting.

Equally enlightening are his memories of the Hollywood greats, his memoir littered with tales of Roger Moore, Billy Wilder, Paul Newman, Steve McQueen, Ringo Starr, Sammy Davis Jnr, Barbara Streisand and of course Jackie Collins, who all trooped in and out of their home for the wild hedonistic parties his mother threw.

“It was the 60s and 70s when permissiveness and experimentation were widespread. People were very focused on fulfilling themselves, and as a kid you don’t question that. But the charisma was mega,” he says.

“So when I look back at the drama of my childhood, it’s so rich, handing me the tools I needed to become an artist.

Seemingly blasé about the resulting indiscretions and voyeuristic viewpoint into their family life, his memoir is also unexpectedly lucid and beautifully written, the artist in him enabling Alex to step back from the whole experience and view it dispassionately, his own behaviour included.

“I just felt it was the right time to open this treasure trove of memories concerning my circumstances, especially during the 60s and 70s when he lived between homes in Beverley Hills and London.

“I have felt the need to tell this story since the age of 18. It was just finding the time to do it. I wanted to share the treasure,” which he will do when he arrives at the Oxford Literary Festival later this month.

As harrowing as it is fascinating, however distanced he appears from it, Alex explains on the book sleeve: “When I look back at the broken storyline of my childhood, I see that the chief culprit was an ogre called Show Business... my parents were enslaved by the monster’s demands.”

As a result Newley and his sister Tara, as well as numerous step-children, were shuttled between homes, nannies, step-parents and schools with all the outward trappings of success and fame, overloaded with toys, shopping trips and gifts to compensate for their parents busy whirly-gig of a social and professional life, yet lacking nurture, care or structure.

Remarkably unbitter about the whole thing, it’s as if Newley is unable to compute the impact his story has on you, the reader. Because while a funny coming-of-age tale, it is deeply sad in parts.

“Yes, getting it all out into the public domain has taken some getting used to but I’m finding my way,” he smiles. “I had to do it properly though and include all the blues, reds, yellows and blacks that I remember because it was such a colourful, vibrant, powerful time.

“So I’ve kept it honest and simple, making sure I get the emotions just right. When you are telling your truth you can give yourself full rein, and then pull it back if it isn’t adding anything to your story.

“You just have to let it flow out and remember how you felt at the time. There were so many things I wanted to talk about and celebrate. It was very empowering.”

His father, the infamous English actor, singer and songwriter, has since passed away, but with Joan as exuberant as ever, presumably he had to get the project past his mother first?

“She said it was my truth and she respected that. She understood that it was from a child’s point of view. And she is a pro and a grown-up so has been wonderful about it all.

“Of course in those days parenting was very different anyway but obviously I have a very strong bond with my sister Tara because we experienced it together.

“And yes I was spoilt; I was showered with gifts inevitably because my parents were making a lot of money and they just wanted to share that with us, because my father grew up in total poverty.”

That Newley managed to pour his considerable artistic talent into portrait painting is something of a godsend, so many celebrity children falling by the wayside.

“Of course there is something to be said for security, but instead I had variety and change and challenges which I now constantly explore in my art.”

It also helped to pad out the book, much of the unspoken sentiment expressed via his art which is scattered throughout.

“It certainly eased me into the book. And I write in a child’s voice because otherwise the whole thing can seem slightly overwhelming so I adopted a child’s point of view and that was the key to unlocking the book, just as a news-writer would approach a story.”

Not that he needed the additional fame or money, his job as portraitist to the stars meaning he is in constant demand from the likes of Dame Judy Dench, Derek Jacobi, Christopher Reeves and Kenneth Branagh, while working on abstract work of his own.

“It all stems from my parents, because they were so colourful, so magic, so watchable. My mother was so beautiful you couldn’t take your eyes off her. But my portraits are about more than that. It’s what makes mu subjects tick. I want to capture their essence.”

As for what’s next, Unaccompanied Minor finishes when Alex chooses to move back to London from LA.

“I didn’t mean to stop there,” he says. “I just felt that when I got on the plane to return to England it was the end of something, so I stopped. But if feels like a complete work.

“I very much hope there is more to come because I have been excited by the response so far. It has been very positive which has emboldened me to keep going and write the next part.

“We are all witnesses of our own life, directing the movie and acting in it and that weird duality. It was a fascinating challenge and it has been an extraordinary journey.”

Alexander Newley brings Unaccompanied Minor: A Memoir, to Oxford Literary Festival on March 18