When the eccentric stars jumped in a van together to rediscover their roots, it led to all sorts of revelations, Georgia Humphreys learns.

Alan Cumming felt very anxious ahead of filming one particular segment of his new travel series.

Channel 4's Miriam & Alan: Lost In Scotland sees the esteemed actor, 56, venturing around his native Scotland in a mobile home, with a new friend in tow - fellow thespian, 80-year-old Miriam Margolyes.

Along the way, the pair visit the house where Cummings was brought up, and where he had to deal with a dad who was "violent and abusive", as detailed in his 2014 memoir, Not My Father's Son.

It's something you don't ever recover from, "you just manage trauma", he confides. He found returning to his childhood home "very triggering".

"I didn't sleep well the night before," continues the star, who won a Tony award for his performance in Cabaret on Broadway in the Nineties, and is also known for US drama, The Good Wife. "We got there, it was very emotional. I couldn't go inside. It was a lot.

"Miriam was lovely and very understanding. I was with all these film crew, so I was very self-conscious, but it was lovely to be there with someone who was gentle and tender about it."

Travelling to where Cumming grew up, and meeting his mother, was also a memorable moment of the shoot for Margolyes, who was born in Oxford.

"He told me a little bit about his early life there and the shocking things that he'd experienced as a young boy, and I saw a very different, and very serious, side to this young man. I found that extraordinarily moving."

Admittedly, it's a surprising pairing to be fronting a TV programme.

"Intergenerational friendship is a very interesting thing that you don't see very often," suggests Cumming.

"We're an oddball couple, but we had a great time," he elaborates.

"To encourage people to maybe think outside the box a little bit more about who they get to know and who they travel with and experiences they have, that was something I really liked about it.

"When I would tell people about, they'd be like, 'What?! You and Miriam Margolyes in a van?' It was varying degrees of horror and confusion, and actually, it's really great.

"It's not generic; that's really nice, to have less cookie-cutter sort of television."

Before making the three-part show, the duo really didn't know each other very well.

When Cumming was in the early stages of planning a Scottish-themed project with Blink Films, he was also doing a play at the Old Vic and ended up appearing on The Graham Norton Show to promote it. Sat on the sofa next to him was the similarly "eclectic" Margolyes, who was chatting about her role in BBC hit Call The Midwife.

"I thought we sparred well, and I thought it would be a good combo, and it was - it worked out really well," he enthuses.

The Hollywood stars - Margolyes memorably played Professor Sprout in the Harry Potter films, while Cumming was a Bond villain, Boris Grishenko in GoldenEye - both have Scottish roots.

This is something they explore in their picturesque journey, which took them from their once mutual home of Glasgow and up the West coast, across the far Highlands, and back down the East side.

But it's their incredibly candid chats as they drive along together which really makes Lost in Scotland such a funny and fascinating watch - and it feels genuine, too.

"It's Miriam showing me parts of her relationship with Scotland and me showing her mine and, and just of a friendship growing, and having a laugh," reflects Cumming.

"There are very tender moments as well. We talk about big things; getting older, stuff from my past and my family, and the history of Judaism in Scotland."

"And being gay and our relationships," chimes in Margolyes, who won a Bafta in 1994, for her role in Martin Scorsese's The Age Of Innocence. "We were very open with each other. It was very personal."

How poignant did it feel to be discussing and celebrating queerness together on the telly?

"Actually, I hadn't really thought about it going in, but two older queer people, it's a pretty rare thing to be the hosts of a show, actually," muses Cumming.

"We're both very frank and open about everything in our lives, but our sexuality, definitely, and so I think that's a positive thing."

It's not just Cumming's family we meet; they had dinner in Glasgow with some of Margolyes' relatives too, where her co-star learns about how strong her Jewish identity is.

"It was really lovely to understand that a bit more and to appreciate that," notes Cumming. "And to see some of the Jewish life in Glasgow that I didn't know very much about, that was really fascinating."

"I'm very proud, both of my Jewish heritage and of my family," says Margolyes. "They're lovely people. My cousin Gloria, who's very old - I think she's in her 90s actually - she was there, and that was wonderful for me, made me very happy."

Other interesting characters the stars meet during their voyage includes a Gaelic rapper, modern witches, and a 'Zen golfer'. There's also a noble Lady that Cumming believes could be his distant relative...

"I thought that it was an unfolding of each other and of Scotland at the same time," suggests Margolyes.

"We're taking in what we were looking at, and the people we were meeting - and we were also discovering each other's personalities and characters and learning about that.

"It's a very rare thing, I think, to have that pleasure, that you really get on with your colleague."

Cumming also likes how viewers will see a "whole holistic view of Scotland, not just the biscuit-tin version".

"I hope that it will make people realise that they've got a jewel on the doorstep, and that they should be going around enjoying the islands and the food and the paintings, the cultural life, the music," follows Margolyes.

"I'm very grateful for this, but I think that the viewers should think, 'you know what? It's there. Let's go and have a look at it'."

Miriam & Alan: Lost in Scotland starts on Channel 4 on Tuesday, 9.15pm.