Louis Theroux is taking a trip down career memory lane.

Or as he likens it, he says, in his head to, "climbing a mountain and then you take a pause after you've had a decent interval of walking and then you sit on a bench and you're like 'Wow, we're a long way up'".

And he is not wrong.

The TV star's career over more than two decades is a colourful and impactful one.

His latest project, a BBC Two series titled Louis Theroux: Life On The Edge, shines a spotlight on it with a look back on 25 years in the industry.

Four, hour-long episodes, each with a different theme, Beyond Belief, Family Ties, Law And Disorder and The Dark Side Of Pleasure, will see him revisit some of his most memorable stories.

Theroux, 50, also unearthed unseen footage from older series such as Weird Weekends, which ran from 1998 to 2000.

"It was really fun going back and opening up the treasure chests of old programmes and seeing how far I've come in a way," he says during a Zoom video interview.

"I think in general what I'm struck by is, how many, because I still feel like a novice in some respect, I still feel like I'm learning how to do this, I still have a lot of professional anxieties whenever I'm starting a new project or just continuing an old project, and so to see how many programmes I've made and how many of them still hold up is really pleasing".

He has tackled topics including Jimmy Savile, US neo-Nazis, Michael Jackson and Scientology in his series and TV specials over the years.

But still, looking back, there were small elements of surprise.

"I didn't expect, but in the first three episodes, is how much they are portraits of America, and all the stories being about America, and the themes", he says, listing them, adding: "All sort of say something, you know, I've always made a lot of programmes in America, but I've never made it explicit what they say about America and here I feel like we're able to do that. It's made me feel like I'm maybe a more serious documentary-maker, which is a good feeling, something I'm not used to".

Last year, he published his autobiography titled Gotta Get Theroux This, which charted his career from fledgling journalist in the early 1990s to BBC regular.

Off screen he hosts a podcast called Grounded With Louis Theroux, which according to BBC Sounds, has been their biggest hit on the service during lockdown.

Featuring interviews with stars including Helena Bonham Carter, Sir Lenny Henry, Boy George, KSI and Miriam Margolyes, Theroux says working on it has been "one of the pleasures" of lockdown.

"Being able to have long form chats with people like Boy George and Lenny Henry via Zoom, and these are people who back in the day I tried to get for When Louis Met, a celebrity series, and who probably very sensibly turned me down and now I'm at place where I feel I can tell those stories of interesting people in the public eye.

"That's another area of enquiry I'd like to go further down, he says, "just the idea of long form chats in which you are getting to the truth with people in a way that's comfortable for them and just connecting with people in different spheres of life in a way that feels unforced and unformatted and free form".

The podcast is part of our conversation in response to asking him what story he still wants to tell.

He explains: "What I have never done is a story about radical Islam and the issue of Islamic extremism. I've tried a couple of times and not got that far down the road. I thought for a while there may be a way of telling the story from the perspective of Isis returnees and I even proposed that about a year ago at the BBC but it eventually got pushed back because of Covid. I would still like to tell that story.

"You know the Shamima Begum type of story, the world of people who were caught up in Islamic fundamentalism... and how we deal with that now and the world of that ideology. I think all of that is massively interesting and obviously socially important, and really upsetting as well".

Begum is one of three east London schoolgirls who fled to Syria to join the so-called Islamic State in 2015, and is fighting a legal battle against the UK after she was stripped of her British citizenship.

And what about lockdown and the last few months of life ever-changed for people across the world due to the coronavirus pandemic, is that a story he thinks he will document one day?

"The short answer is I think I might do, but it would be probably in print. I've been keeping a diary, I've had so little time in the last few weeks, I've started to think I'm not keeping enough of a diary," he explains.

There may be, he muses, a "glut of books" written in the next year or year thereafter about this all.

"If I did anything on lockdown I think the only way for me of telling the story would be through the medium of a book or print in which I would excavate the weird tensions... you know in lockdown I was just here with my family, working, but just trying to get through the day, without one of us losing their minds due to this feeling of there not being enough hours in the day, kids being home-schooled or not home-schooled, would be more accurate.

"We have three boys and my wife (Nancy) and I both work, and had professional commitments and you know we're trying to get meals, get everyone fed, keep the house in some semblance of order, get clothes cleaned, do two jobs that are very demanding and then make sure the kids aren't on screens the whole day, it was extremely stressful.

"I think a lot of people had different lockdowns, that was our lockdown, and so, the nature of the arguments we had was kind of interesting, so I started keeping a journal which I talked about (earlier)."

Louis Theroux: Life On The Edge airs on BBC2, tonight, 9pm