Miriam Margolyes surely has one of the film industry’s most delightful speaking voices. It’s an accent so quintessentially British that the actor has admitted to occasionally trying to obscure it to sound less posh. But despite that distinctive Oxford timbre – and her near-lifelong residence in the UK – Margolyes has been an Australian citizen for almost 10 years now.

“I became a citizen because my partner of 54 years is Australian, and I wanted to be able to come and go without having to get visas,” she says. “Rather like my mother when she married my father, she didn’t love him, she wanted to be a doctor’s wife. Well, I wanted to be someone who could come and go. But now I love Australia and I want it to be better. That’s why I make critical programs.”

Her latest is Miriam Margolyes Unmasked, a three-part ABC series that sets out to understand what a “fair go” really means in Australia today. The documentary, which premiers Tuesday 19 July on ABC, will see Margolyes attend everything from polo matches to bogan burnouts as she explores how equitable Australia really is. It’s a gentle prodding she thinks we need, to “see things in a slightly different way”.

“Australians have a very puffed-up idea of themselves,” she says. “They think Australia is the best country in the world, that everything is perfect and it’s the lucky country.”

While this gig may see her step into the role of TV host, Margolyes built her career as an actor. Depending on your age, you may know her either from her role in Martin Scorsese’s The Age of Innocence or as Professor Sprout from the Harry Potter films – though those are just two roles of many.

Before becoming a star Margolyes had film idols of her own. As a child, she would line up outside venues to ask actors like Marlene Dietrich to sign her autograph book. Here, Margolyes tells us about why she’s held on to that sentimental book, as well as the story of a few other prized possessions.

What I’d save from my house in a fire

One of the most precious things I have in my house is an oil painting portrait of my father. It sits in my study, in pride of place behind my desk, and I love it. If I grab that picture, I’ll feel I’m in touch with everything that went before. And it’s very light so it’s not difficult for me to grab. I could just lift it off the wall and scoot out. It was painted by Anne Christie, who I’ve known for a long time.

I got Anne to paint this because I thought I ought to have a picture of my father. Daddy didn’t like the picture, actually. He said, “Oh, it makes me look so small.” But he was small! He was a small man. It’s accurate.

I also collected autographs in a book when I was a little girl, so I would have to grab that as well. I don’t look at it very often but it’s just irreplaceable, and I have the signatures of people like Laurence Olivier and Marlene Dietrich.

I got Dietrich’s autograph when she came to England to do her show at the Golders Green Hippodrome, which I believe is now a television studio but was, in those days, rather a good venue. I queued outside along with all the others and she came out looking impossibly glamorous, and sat on the roof of a car that had come to fetch her to talk to everybody for about an hour. She was utterly fascinating and compelling, and she signed my autograph book and kissed me. It was thrilling.

My most useful object

My walking stick. Quite recently I developed something called spinal stenosis, which is a narrowing of the spinal column. And it means that I walk very poorly and with difficulty.

I actually have two sticks. If I didn’t have them, I couldn’t really walk. And I like to be able to walk. They’re just from the NHS – very ugly, but very vital.

The item I most regret losing

I think it would be my little pocket diary, in which I’ve got all my appointments and everything, which I very recently lost. I’m still in shock that I’ve lost it but there’s nothing I can do.

I will get another one but this has really been a blow to me because I write everything in it. It’s a datebook, not a journal – I haven’t got time for that. I’m living life, not writing about it.