Periscope up: Richard Ayoade and Alex Turner unite their talents in hot new Brit flick Submarine

"Wow," says Richard Ayoade in the un-wowed way the actor/comedian/writer/director says most things, "this is like couple's therapy." Turning to Alex Turner, he deadpans, "I really appreciate your candour..."

"I just wish he wouldn't do that thing," begins the Arctic Monkeys' singer-songwriter with a heavy sigh as he fingers a packet of Camel Lights. Then they both laugh.

"This is new, this," says Turner with a chuckle, glancing at Ayoade, who is sitting next to him on a ratty couch in a spartan room in the unshowy central London offices of Warp Films. As frontman with the best new British band of the past decade – even if they are a band known for their reluctance to play the PR game – the 25-year-old Turner is familiar with the interview situation. But he is less used to taking part in two-hander conversations with artists from other disciplines, albeit an artist who's a long-standing friend and collaborator. And certainly this is the first and only time he'll be discussing at any length his latest musical project: the soundtrack to Submarine, Ayoade's big-screen directorial debut, for which Turner has written all the songs.

When he was considering asking Turner to help out with the music on the film he began shooting in autumn 2009, Ayoade's only concern was "imposing, and going, 'Can you do a load of work?' We knew each other quite well by then, but I was worried – it's a bit like asking someone to help you move house. Does he really need to be writing more songs now? Maybe he wants a break from an album a year? 'Alex, can you sneak in another five songs?' That was my only worry – that I was taking the piss."

But in the end, "It was the best bit of it," continues the star of Channel 4 sitcom The IT Crowd, of Turner's bespoke contribution to his adaptation of Joe Dunthorne's 2008 comic novel about 15-year-old Welsh lad Oliver Tate and his pyromaniac girlfriend Jordana Bevan. "It was just like getting good stuff for free. I did nothing and it made my film a million times better. That's the dream collaboration: you do nothing and the other person is great. That's how I want every film to be from now on. Alex's music was the thing I worried about least."

"I don't think it's summat I'd be comfortable or feel qualified to do, a film soundtrack," says Turner in his broad Sheffield accent. "I wouldn't really know where to start. And now, if somebody tomorrow asked us to do one, I don't think I'm the man for that job, really. But this was an exception. I'm mates with Richard, and the way it came about, it were like a natural process."

Both men are friendly and chipper, but neither is the most loquacious of interview subjects. Each talks in occasionally jumbled syntax; each is happy to let a sentence or thought dangle or drift. "I'm fading myself out here," says Ayoade at one point as a particularly long thought takes it out of him. Nor are they ones to blow their own trumpets. But they do submit to 75 minutes' probing with good humour, some seriousness, flashes of irreverence, much warmth and a dash of self-mocking.

All of which qualities are of a piece with Submarine. It's a vivid, insightful and very funny portrayal of small-town adolescent angst. Think Juno meets The Secret Diary of Adrian Mole (enthusiastic cineaste Ayoade prefers to reference Eric Rohmer's Love in the Afternoon). There are brilliant performances from newcomers Craig Roberts and Yasmin Paige. And from Paddy Considine (playing a mullet-sporting life coach), Sally Hawkins and Noah Taylor (playing only child Oliver's buttoned-up parents). And from Alex Turner's five songs: naturalistic, easygoing and largely acoustic-based, they both complement and amplify what Turner calls the "temperature" of Ayoade's film.

In the Ayoade/Turner interview environment, relaxed as they are in each other's company, the temperature might take a little warming. But they get there...

Why was Alex Turner the man for the job?

Richard Ayoade: "Um. Well. Ha ha. I liked the songs Alex had done previously. It was him or Jay Kay [of Jamiroquai]. It actually came down to a coin toss in the end. It was the only fair way to do it. But, no, I wasn't worried that the lyrics would be weak. That wasn't a concern. There was no Lars von Trier meddling – he wrote the lyrics to [Björk-starring musical] Dancer in the Dark."

Alex Turner: "Originally I weren't gonna write songs for it, though. We were talking about cover versions..."

RA: "...like a Scott Walker does Jacques Brel thing. Or Serge Gainsbourg. But I think probably I secretly k hoped that it would fall through. But it feels a bit presumptuous saying, 'Can you write five songs?'"

AT: "That were it. Like, if originally Richard had said, 'Can you write some tunes for this film?' I'd probably have gone west. I think that would be a difficult thing to do. But the way it worked was, we first discussed doing covers. He liked the idea that it would be one musical voice through the film, like in The Graduate."

Did you get as far as picking any covers?

RA: "We had various ideas. There were some John Cale tunes – 'Fear is a Man's Best Friend', 'Big White Cloud'. There was that Nico tune – 'I'm Not Sayin'. And we had this cover of [Irving Berlin's] 'How Deep is the Ocean' as well."

AT: "Oh yeah, I forgot about that. We recorded that."

RA: "There were these two bits in the film where there were going to be two songs played in their entirety. That was, I suppose, like The Graduate – when you have 'The Sound of Silence' and 'April Come She Will' actually played back-to-back – rather than the usual soundtrack thing of a minute of music then fade it out... Or you have a song played over a montage – a girl steps out of a car with Aerosmith's 'Dude Looks Like a Lady' playing..."

AT: "Or 'Rebel Yell' by Billy Idol."

RA: "It just felt better to not have any pre-existing [musical] material in it. So when you hear a song, you don't have a lot of baggage of things you associate it with. So it felt that covers would be a way of getting around it – instead of having the Nico version, you'd have Alex's new one. And also just because I suppose that's been done quite a lot – the mix of a director's favourite songs."

Wes Anderson has made an art of it.

RA: "Yeah, and Tarantino. The Wes Anderson ones are really good. But they're very much [soundtracking] montage bits. And there are a lot of them. Nico now just is The Royal Tenenbaums. She's so Wes Anderson, it's almost against the law to use Nico in a film now."

Fresh off a world tour in support of Arctic Monkeys' third album, 2009's Humbug, Alex Turner was at home in New York – he and his girlfriend Alexa Chung lived there temporarily while she pursued an American TV career – and, as an inveterate songwriter, began fleshing out some new ideas.

"I had some tunes that I'd been sitting around playing," he remembers. "I never thought they were really gonna be Arctic Monkeys tunes, just because it were me picking at an acoustic guitar. And that's definitely not what Monkeys is about." Nor is it the style of the Last Shadow Puppets, his side-project with best friend Miles Kane. "It were just songs that I didn't really know what they were gonna become..."

After the rigours of touring in support of the band's heaviest album, Turner found the more relaxed playing and writing style "refreshing". He'd already read Dunthorne's novel at Ayoade's urging, and, over the internet, had been watching the rushes from the film set in Wales.

With his new compositions, "There was something about 'em – quite sparse, just letting the song be the focus. I had a couple, 'It's Hard to Get Around the Wind' and 'Hiding Tonight...' It just occurred to me maybe I should play them to Richard, see what he thought about them. Then I wrote a couple more – not necessarily thinking, 'Oh, I'm writing specifically for that film.' But I had it in mind..."

This brings us to a question that Joe Dunthorne gave me for Turner, creator of "I Bet You Look Good on the Dancefloor", "Mardy Bum" and other richly melodic tales of narrative piquancy. The author wanted to know how "closely or otherwise" he worked to the scenes shot by Ayoade when he was writing Submarine's songs.

"Not really that close at all for the most part," Turner replies. But when it came to recording the songs – last April, in a tiny studio near London Bridge, with Turner and regular Monkeys producer James Ford playing most of the instruments (Bill Ryder-Jones, formerly of the Coral, also helped out on guitar) – "The edit of the film was much further on. So Richard came down, and we played with some of the structures of the songs to make them fit a bit better, in terms of the length being right. But yeah, in terms of lyrics, I wasn't sitting there with pictures trying to match them."

But there were some "flukes". In the echoey, music-hall lament "Stuck on the Puzzle", Turner sings of "fingers dimming the lights", while in the film, a turned-down dimmer switch alerts Oliver to the fact that his sad-sack parents have been having sex. k

"And there's a thing about how they 'want the world on a dessert spoon'," notes Ayoade, "and it was just luck that when we were editing it, the song landed on an image of a dessert spoon next to some custard. But I like it when it doesn't feel like something's tied to the pictures. It was the same with Andrew Hewitt's score – he did a lot of it without the pictures. Because it can get a bit dum-dum-dum-dum, like Desperate Housewives.

"That [kind of film music] makes me sweat," continues the former president of Cambridge Footlights and one-time stand-up. "It just feels so jaunty and teen-picture. I really like it when you have the music as a sort of opposite. So when they're running around during [the gorgeous lament] 'Hiding Tonight', all the stuff they're doing is quite violent. I like that. I guess it was a bit like that video we made for 'Fluorescent Adolescent' – you have something very violent juxtaposed with the song. You go off in the other direction."

When Alex Turner and Richard Ayoade first met, they bonded over a handful of things: The Sweeney, clowns and a desire not to plump for the obvious.

The singer and his bandmates were looking to make a video for "Fluorescent Adolescent", the second single from their second album Favourite Worst Nightmare (2007). The actor, at the time best known for playing computer geek Moss in The IT Crowd, was looking to broaden his experience as a director.

"That was the first time we'd put out a single like that," recalls Turner, "major key and quite poppy. We were probably a bit reluctant to do that. And almost as part of, like, a condition of putting the single out, the deal was that we'd have a video that was sorta the opposite of it."

"I think the band wanted clowns," says Ayoade, 33, born in England to a Norwegian mother and Nigerian father. "Often with a video, people say they want this story and this one idea, and you think of a structure for it. So clowns were a prerequisite – maybe cos there was a fairground-y sound to some of the song."

"That was it, there was bit of that," nods Turner. "And maybe Jamie [Cook, guitarist] was quite up for there being a scrap..."

The video's storyboard was set: fighting clowns going comedy toe to comedy toe on some waste ground. At the Sheffield home of Warp Films producer Mark Herbert, band and director clicked as they watched clips from The Sweeney (for the "vibe" of the action favoured by Ayoade) and Superfly (for the feel of the punch-ups).

And the bond went beyond that. The camera-shy Arctic Monkeys didn't want to be in the video; the celebrity-phobic Richard Ayoade was diffident about both his own small-screen fame, and about the normal models – Lights! Action! Fireworks! – for pop videos. "It's still our favourite video," nods Turner.

It was the start of a firm friendship and a fruitful working relationship. Turner and Ayoade would go on to work together on two more Arctic Monkeys videos (for the Humbug singles "Cornerstone" and "Crying Lightning"), a concert film (At the Apollo) and two videos for the Last Shadow Puppets ("Standing Next to Me", "My Mistakes Were Made for You").

"Richard wants it to be tasteful and it's got to look right," says Turner of Ayoade's aesthetic, which has also been put to good use in videos for Yeah Yeah Yeahs, Kasabian and Vampire Weekend. "Yeah, I suppose there is a parallel there with us."

Ayoade also understands the sense of humour of the band who dressed up as characters from The Wizard of Oz and as Village People to accept their Brit Awards for Best British Band and British Album in 2007, for their debut album Whatever People Say I Am, That's What I'm Not. In the purposefully low-fi "Cornerstone", he filmed Turner – resplendent in a sensible red jumper – addressing the camera and dancing a choreographed dance. In "Crying Lightning", the director made the band giant-sized and put them in a boat in stormy seas.

AT: "We were quite into being on a green screen in that one."

RA: "Yeah, a bit Lord of the Rings... I think the idea was to have a very over-the-top video, with them as giants. I always think that's quite funny in music videos, cos it's such a pompous thing to do. Like in the Jackson 5's 'Can You Feel it'."

AT: "That was the reference we wanted..."

RA: "I remember one comment was that the band had gone really 'MTV Rocks video' – but it was just a stupid idea."

AT: "I think our music's usually got humour in it. We try to carry that over to the videos."

RA: "Then in 'Cornerstone', the idea was to do the complete opposite, and film it on a camcorder..."

AT: "...try to make it like a non-video. But that video was definitely summat we could have only done together. I was probably still reluctant doing it even with Richard. We did a version of it in his living-room one night, where I just couldn't get through it without laughing. It was the same when we actually shot it – both cracking up, trying to keep a straight face as I did a little pirouette."

It's nearly time to go. Submarine has a healthy critical tailwind – it was well-received at the Sundance Film Festival in January – and Ayoade, gentle, fidgety soul that he is, has more promotion to do. Turner and the rest of the Monkeys, meanwhile, are in the final stages of mixing their fourth album, Suck it and See. Recorded in Los Angeles in January, it will be released in June. A few days after our interview, the band's website suddenly presents a video for a new song, a heavy, 1970s-style blues-rock number called "Brick by Brick".

There's just time for two questions from the film's lead actor. Craig Roberts wants to know whether, given the chance, would Richard Ayoade have replaced him with Juno star Michael Cera?

"Yeah!" beams the director. "I'd always say on set that essentially I was going to recast with Michael Cera and [fellow Juno star] Ellen Page if Craig or Yasmin did anything wrong, that I had both of them on speed-dial, that Cera was literally a chopper ride away."

And the 20-year-old's question for Turner: "How have you got through life looking like me?"

"Yeah, that is odd!" laughs the musician of the uncanny likeness between him and the young actor. "When we went to the cast-and-crew screening, which was where I met him for the first time, Craig came up to me and said, 'You do realise we look an awful lot alike?' Quite funny. But yeah, he actually looks like my dad when me dad was younger. We took some pictures together and showed 'em to me dad..."

"Was it like in Back to the Future when Marty McFly meets his own dad?" wonders Ayoade.

Suck it and See features a new, full-band version of Submarine song "Piledriver". That track aside, does Turner think the experience of writing this fist of songs for Submarine has fed into the songs on the new Arctic Monkeys album?

"Absolutely. It always does, I've come to realise. It's not like they're that far apart, in terms of when I came up wi' 'em. But obviously the difference is, those songs that are on the new Monkeys album have been through that mill – you know, the other three lads in the band. But in terms of songwriting, I think always one thing's built on the last."

Ayoade's not so sure. "It's all reggae, from what I've heard."

Turner laughs. It's not, "but [Queens of the Stone Age's] Josh Homme sings some backing vocals on the album. You heard it here first."

'Submarine' (15) is in cinemas now