Hollywood actor Jay Baruchel is a massive fan of the veteran Scottish indie band. To prove it, he even appeared in the video for Every Little Means Trust, the new single from the group that he says soundtracked half his life. Join the love-in, backstage at the Camden Roundhouse

It is the least likely pairing of a Hollywood star and a British indie band since Gwyneth Paltrow and Chris Martin consciously coupled. Jay Baruchel, the lovable nerd whom Vanity Fair hailed as the only serious rival to Michael Cera in the “adorably unthreatening man-child that makes all the emo girls swoon” stakes, has appeared in Clint Eastwood movies (Million Dollar Baby), romcoms (She’s Out of My League), sci-fi films (RoboCop), satirical action flicks (Tropic Thunder) and DreamWorks computer animations (How to Train Your Dragon). He’s an associate member of the Judd Apatow-Seth Rogen dream team, has written a successful sports drama (Goon), and is the main character in his own sitcom (Man Seeking Woman).

So why is he in a north London music venue, hanging around backstage with Idlewild, the Scottish group whose main claims to fame are two Top 10 albums in 2002 and 2005, and NME’s description of their early ramshackle din as “the sound of a flight of stairs falling down a flight of stairs”? Because he has been invited to appear in the video of their latest single, and he couldn’t say no – they’re his favourite band of all time.

“It sounds super-pussy to say it, but it’s been the soundtrack of my life for close to half of it,” says the 33-year-old actor, whose surname means “blessed is the one” in Hebrew (his father is Jewish, his mother Irish-Catholic). He explains how he fell in love with the band, his skinny frame perched precariously on the edge of a dressing table in a changing room in the Roundhouse, where Idlewild are due onstage in two hours. Meanwhile, frontman Roddy Woomble and guitarist Rod Jones, sitting in chairs, are models of calm next to the hyperactive Canadian, their phlegmatic delivery in stark contrast to his staccato fire. Baruchel explains how he got here.

“One of my best friends went to the University of Bristol and I’d visit him,” he says. “I was just fucking around with his computer in the dorm and You Held the World in Your Arms [from 2002’s The Remote Part] came on, and I was like: ‘Holy shit, what the fuck is this?’ I went home and bought everything I could by them.”

Baruchel was 19 at the time, at that formative stage when you break up with your first girlfriend. He laughs nervously, as though his secret diaries from that period have just been ransacked. Presumably Idlewild’s music – which he calls “melancholy yet triumphal” – would have been ideal for such moments?

Watch Jay Baruchel in the video for Idlewild's Every Little Means Trust Read more

“Indeed they were,” he replies. “They saved my life a shitload of times.”

In fact, he says, when it comes to women, Idlewild have since become the acid test.

“American English [from The Remote Part] is my litmus test for chicks I’m dating,” he admits. “If they can’t fuck with that, there’s no point.

“These are fuckin’ models, man, they’re fuckin’ battle cries,” he says of Woomble’s lyrics, addressing him with a passion that suggests he’s going to climb down from that table and kiss the singer flush on the mouth. “I use your words to describe shit in my life. Like, ‘Young without youth’ from American English – that’s fuckin’ spot on! I know dozens of people that would fit that bill. By the end of that song it feels like you’ve just finished an awesome book.”

Woomble is flattered – he doesn’t get many celebrity fans where he lives, on an island in the Outer Hebrides with only 100 inhabitants.

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“It’s nice that people are still interested,” he says of the band who formed in 1995, partly as an antidote to Britpop. “Twenty years is a long time, but there seem to be more people interested than ever. Our recent album [Everything Ever Written, self-released in February] went Top 10 and we’re not even on a label.”

He considers Idlewild the last of a dying breed. “These days you’re expected to give everything away for free,” he says. “But we were a pre-internet band – we made 7in singles and actually sold them! We’re from the last generation of bands who toured to promote records because the records would sell. Now, of course, it’s the other way round – you basically put records out so you can make money from touring.”

With 3,000 paying customers waiting outside the Roundhouse to enjoy Idlewild’s increasingly mature and resonant sound – in the early days they were influenced by American hardcore bands such as Minor Threat and Black Flag, but since 2005’s Warnings/Promises the comparisons have been with REM – Woomble concedes that “big cult attraction” best describes them. They inspire slavish devotion – Baruchel isn’t the only one travelling continents to be here. As Jones reveals, there are fans coming from Australia and Japan; even a Virgin Atlantic pilot who uses his free air miles to follow the band. Jones and Woomble agree their appeal lies in the tension in their music between sadness and euphoria.

Facebook Twitter Pinterest Idlewild: ‘‘We were a pre-internet band – we made 7in singles and actually sold them!’ Photograph: PR

“It’s puritanism and hedonism pulling against each other – that classic dualism that is so much a part of the Scottish psyche,” Woomble says. Jones is nonplussed by crowd reactions, especially when it’s “Mancunian beer boys in the front row wailing along with the choruses”, but then, even Joy Division, another of Baruchel’s favourites, attracted a beery contingent. As he points out: “Even weirder is that in East LA you get these hardcore Mexicans who are obsessed with Morrissey. He’s an icon in the Mexican community – it’s insane!”

For Baruchel, Idlewild’s “quintessentially Celtic combination of hope and melancholy” offers a ray of light. “I try to experience life to the full,” he says. “That being said, there’s a massive chip on my shoulder, for sure.”

Where does that come from? “Oh Jesus,” he says, preparing to recite a litany: “Being the son of an immigrant, being of mixed ethnicity, being undersized … A lot. I’m surprised more people don’t have chips on their shoulders.”

When pushed for a definition of his own work – especially the material he writes with his partner Evan Goldberg, notably 2011’s violent Goon – he goes for “heart and teeth”. “We want people to give a shit, but we also want to hit them in the side of the head with a two-by-four,” he says.

As for Idlewild, they “stand for different things over the years”, according to Woomble. “We were 18 when we started; we’re 38 now. We’re building up a body of work that describes who you are over a long period of time.”

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Baruchel and Idlewild only met for the first time at the start of this interview, having become acquainted via Twitter, but already they can imagine being friends. Ice is broken further when Baruchel poses some questions of his own, including some absurdist word association (for the record, “cheese skirt” makes Rod Jones think of “some kind of pig”), the cause of much hilarity. But Baruchel’s ardour for Idlewild is no joke. And although the actor is the more famous, he is clearly the more starstruck.

“It’s so strange,” he confides as he and the band head off for a pre-gig meal. “I watched them at soundcheck and I can mouth every fuckin’ word.”

He is excited about the show, even if, he suggests, “I’m going to be an embarrassing mess”. Woomble promises that “there won’t be any stage-diving – the crowd are too old for that”, but tears are on the cards. “There’s a very big chance that I’ll well up at some point,” admits Baruchel.

Finally, I ask whether there is a shared sensibility that carries across their work.

“We’re all creating shit,” ventures the actor. “We’re all trying to say something ideally, trying to be honest, or at least truthful. And we’re all trying to sell it, otherwise we’d just doing be doing it in our bedroom. You want people to fuckin’ see it. The poison of commerce comes into it a little bit, and you’re constantly having to walk the fuckin’ tightrope. But yeah, the shit is very similar.”

The single, Every Little Means Trust, is released on 27 April. Everything Ever Written is out now on Empty Words.