Joanna Lumley's absolutely fabulous journey from Purdey to Patsy - and finally Sheffield

The unmistakeable voice on the other end of the line – surely one of the most recognisable voices in the UK – may be a little weary initially, but she soon perks up when we start to talk about her appearance at Sheffield DocFest this weekend. “I can’t wait,” she says. “I’m looking forward to it more than I can tell you. I just love documentaries. I am absolutely thrilled to have been asked – it’s a real privilege.”

Although probably best known in recent years for her role as fantastically louche fashionista Patsy Stone in all five series of Jennifer Saunders’ hit TV comedy, Lumley has had a varied and diverse career – taking in everything from Bond movies to appearances in Coronation Street and Steptoe and Son to her breakthrough role as Purdey in The New Avengers in the 1970s – and over the past quarter century or so she has built up an impressive portfolio of top-quality documentaries, which she will be speaking about at the Crucible Theatre on Sunday.

As long ago as 1991 Lumley travelled to Malaysia to explore the legacy of the legendary British rulers of the jungle kingdom of Sarawak for the film In Search of the White Rajahs and was memorably sent by the BBC in 1994 to a desert island in Madagascar for a week for Girl Friday. Building her own shelter and foraging for food, she was left entirely on her own on the island every night while the film crew returned to the mainland. She’s certainly not afraid of roughing it; quite the opposite, in fact. “The bits that I find most interesting are places that are off the beaten track,” she says. “And living in huts and tents – I once spent some time staying with Mongolian goatherds and I loved it. That sort of thing I find much more thrilling than staying in a posh hotel. I really like doing the tougher parts – I think I’m a tramp at heart, really.”

Recently she has made a number of prestigious multi-part travel documentaries for ITV including taking a journey up the Nile in 2010 from the sea to the source in Rwanda. “Following the river through all those extraordinary countries was amazing,” she says. “In particular North and South Sudan – we were there just before they separated so there was a great deal of tension at the time.” She followed this up with Joanna Lumley’s Greek Odyssey in 2011 which explored the past, present and ancient history of Greece including its influence on western culture. And she delved into the story of Noah’s Ark in 2012 which involved travelling across three continents.

“I suppose for me it’s a curiosity about the world and people and places,” she says of her travelogues. “I’m fascinated by history and geography and where they overlap.” And with her warm, informative delivery style she makes a perfect travelling companion.

“The best way to do these things is not to try and learn lines or keep to the stuff you already know – of course you have to include some facts because people expect that, but I don’t like to be too over prepared,” she says. “I like to ask questions in the spirit of true enquiry and that helps to encourage people I’m interviewing to speak honestly so that the viewer may be told about things they might already know but see them from a different perspective. You want to be the viewers’ friend; you are going on a trip together. They doesn’t want pompous speeches but equally they don’t want to watch me just saying ‘gosh, this is awesome’, so it’s about getting the balance right.”

Lumley says it’s difficult to choose one moment or voyage that has left the most lasting impression on her but if she had to pick a favourite she says it would probably be travelling to Norway in search of the Northern Lights for a BBC one-off in 2008. “That does really stand out for me as one of the most exciting trips I’ve made,” she says. “It was a short shoot over eleven days and when we got to day eight and we still hadn’t seen the lights I was beginning to get a bit worried we might not see them at all – and then we got this absolutely amazing light show that I will never forget.”

Two years ago she was invited by American pop icon will.i.am to interview him at his home for an hour-long BBC documentary and last year she made both her three-part series Joanna Lumley’s Trans-Siberian Adventure – which saw her travel the 6,400 miles from Hong Kong to Moscow along the famous Trans-Siberian Railway – and an intimate and very personal profile of the King of Rock n’ Roll in Elvis and Me.

“I am such a fan of Elvis, you would think that I had begged to do that film,” she says, laughing. “But actually quite by chance Sony were re-recording his backing tracks at Abbey Road and they came to me knowing that I pretty much have ‘I love Elvis’ stamped on my forehead.”

It is an affecting film that sees Lumley tracing Presley’s journey from very humble beginnings to international superstardom. “You do get closer to the subject when you are doing something like that,” she says. “Going to the humble little hut in Tupelo, Mississippi where he was born really does make your heart beat faster. And it was extraordinary to sit on the same window sill where Elvis sat and played his guitar when he was a teenager.”

She has just finished filming in Japan for another documentary for ITV. “It was fascinating,” she says. “There are a few things we think we know about Japan – like sushi, Hello Kitty and Toyota, but I hadn’t any idea about the thousand earthquakes that happen every year and the over four hundred smaller islands on the archipelago. We started off in the North and went all the way down. Over the three episodes I think we tell a really fascinating story.”

It’s scheduled to screen later this year – in the meantime there’s more Ab Fab promotion to do. Once they finish in the UK, they are off to America and Australia to promote the movie there. She says that working on the film was a great pleasure – and it sounds like it was an enjoyable reunion. “It was tremendous fun,” she says. “We all love each other so much – the core five, the five Js – June Whitefield, Jane Horrocks, Julia Sawalha, Jen and me. Then there were lots of people who appeared in various episodes over the course of the five series and we also have around sixty celebrity cameos, so it was really good fun.”

And her fondness for Patsy certainly hasn’t diminished over the years. “I love her,” she says. “The second the hair goes up, and the cig goes in the mouth and the voice deepens, I’m just really happy.”

• Joanna Lumley is at Sheffield DocFest on June 12 at 3pm at the Crucible Theatre. www.sheffdocfest.com The festival runs June 10-15.

Absolutely Fabulous: The Movie opens in the UK on July 1.