Roseanna Brown: "I remember thinking, 'We're all just doing make believe for a living - and that's amazing!"

"A glorious pop song with R&B-inspired guitar and smooth, passionate vocals aboard a carousel of love." That's the Hot Press Irish Songs crew extolling the musical virtues of 'Awake', the recent banger from Roseanna Brown.

What they couldn't tell you in a pithy one-liner is that the Los Angeles-based British-Irish actress is also a talented actor who made her big screen debut as a teenager in Harry Potter And The Deathly Hallows: Part 2 and is currently to be seen alongside Andrew Scott, Brendan Fraser, Damien Lewis and Kerry Condon - class cast or what? - in new World War II D-Day thriller Pressure.

Oh, and that the 1970 Eurovision Song Contest winner, Dana Rosemary Scallon, is her auntie. "I was born in London, but my mum's side of the family is from Tipperary and Mayo and my Dad's from Derry, which every Easter and Christmas break we went back to," Roseanna tells us. "We used to take part in the Feis and the other musical competitions they had there. That was from when I was five until sixteen, so it feels like I half grew up in Derry."

Roseanna is a child of the early '90s, which means she experienced The Troubles. "I remember us going over in '96/'97 and me, my sister and brother getting caught up in bomb scares - like when we went to the cinema but didn't get to see the film," she recalls. "We'd be stopped at all checkpoints and found ourselves in situations where our strong British accents were definitely not an advantage. I tried doing a Derry one but it was rubbish!

"When people in the States ask me about where my family's from, I say 'Have you seen Derry Girls? Because that's a great representation of them.' I made my (American) husband watch it and he was like, 'Okay, I get it so much more now!"

When did Roseanna realise that her Auntie Rosemary was different to other aunties? "As a kid I remember going out for a wander in Derry and people just lighting up when they met her," she resumes. "Auntie Rosemary always went out of her way to talk to them because she realises how it brought people together during very dark times."

My politics couldn't be more opposite to hers, but when I met Dana one day in NewsTalk she was absolutely charming. "Oh, my politics too, but she doesn't care!" Roseanna laughs. "No matter what you believe in, she will treat you with absolute respect and kindness."

Roseanna was still a teenager when she got her big break playing a Slytherin student in Harry Potter And The Deathly Hallows: Part 2. "I was doing my GCSE exams and mum had to get permission for me to take time off school. Thankfully, they said 'Yes!' It wasn't like 'Come be an extra', they auditioned every single one of the kids they wanted to be around the main cast. There were specifications for each house which you had to 100% match."

I imagine it was and remains the biggest production she's been involved in. "For those Battle of Hogwarts courtyard scenes, there were hundred and hundreds of people," a still awestruck Roseanna says. "They pared us up with a stunt person for battle wand training. We had to learn the moves which went with certain spells. I can mentally be there now...but at the same time it's still a blue, if that makes sense!"

It does! After Harry Potter, Roseanna ticked another acting box by entering the Marvel Universe and bit-parting in Thor: The Dark World. "I remember thinking, 'We're all just doing make believe for a living - and that's amazing!" she laughs. "They gave me the title of 'Fandral's wench' which didn't go down well with my mum who was like 'What is this film and what does wenching entail?!' It was okay, though, when she realised it was Marvel.

"I got the role without knowing beforehand what the film was or seeing the script, which I should have been sent but wasn't. The people I was mainly around were Chris Hemsworth who's absolutely lovely, and the lovely Zachary Levi who was on a hot streak having just done Chuck. Daniel Radcliffe's stunt double, who I knew, was on that too so it was a lot of fun."

Having concentrated for a while on her music career - more of which in a moment - Roseanna absolutely knocks it out of the park in Pressure, which revolves around the role meteorologist James Stagg and his fellow weathermen playing in the D-Day landings going ahead on June 6, 1944. "We know what the ending is but it's still really tense!" she enthuses. "On set, the director Anthony Maras had a clock ticking down to recreate the stress they'd have been under in the D-Day control room. He'd also say 'action!' without any warning to make it feel like you were on the frontline. That really translates onto the screen."

What was her World War II history like before that? "Not as good as it should've been," Roseanna admits. "I didn't know about D-Day being pushed back a day or the gap in the weather. Watching it I was like, 'Oh my gosh, imagine if that had gone wrong? That's really trusting your team and their expertise.' Just the amount they were able to do back then without the technology we have now."

Come awards season, don't be surprised if Pressure receives multiple Best Cinematography nominations. "When you see the beaches and the warships, it's real footage they got from the War Museum and seamlessly blended in," she marvels. "I'm not really up on the technical stuff, but it's insane how good the finished film looks."

She has similarly positive things to say about her co-star Damien Lewis. "After we'd done the first couple of takes he came up to me, introduced himself and said, 'You're doing very well!' We chatted for a bit about how this was previously a play, and then everyday he'd say, 'Hi Roseanna, how are you doing?' Damien actually wanted to bring me into the scenes, which was so lovely of him. Andrew Scott as well was just brilliant."

Returning to matters musical and 'Awake' is the result of a '21 Songs In 21 Days' challenge Roseanna set herself. "They also had to be fully demoed by the end of each day so no pressure!" she laughs. "Awake' was Day 18, by which time it all felt like a fever dream. I hadn't written on my own for such a long time and wanted to rediscover my voice, which had been diluted a bit by all the collaborations I've been doing - even if those people are wonderful to work with. The best thing to come out of it is that i absolutely trust my gut now."

While she can't name names, several major K-Pop acts have covered Roseanna's songs but not yet released them. "It's a real waiting game," she sighs before adding: "K-Pop is the most freeing form of songwriting: 'What about this and this and a rap section? And, ooh, what about a hook melody there?' It's an especially good way to exercise the lyrical mind because they want words that stand out."

Before embarking on her solo career, Roseanna, her sister Alanna and her brother Jonathan came tantalisingly close to breaking Europe and States as The Rua. "It was all going really well...and then Covid happened!" she sighs. "We did a massive tour with Westlife which was partly down to Louis Walsh knowing Auntie Rosemary for a very long time. I met him as a little kid when they were doing the Song For Ireland together. He's always been a big supporter and willing to share his knowledge of the music industry, which is vast.

"Even though we didn't have that elusive hit, running round the world with my brother and sister was one of the best experiences of my life."

• Pressure is in cinemas now. See Roseanna's Insta for musical updates.