Alex Lawther and Jessica Barden bound towards each other in a basement boardroom in Channel 4’s London offices and hug like long-lost siblings. “I’m wearing my End of the F***ing World necklace,” Barden tells Lawther proudly, pointing to one of those heart pendants you break apart and share with a friend. Lawther shakes his head. “Ah, I didn’t put mine on today,” he says, sounding as if he’s committed a mortal sin, “but I’ll definitely wear it to the launch”.

The End of the F***ing World review – coal-black comedy makes a killer return Read more

It is a far cry from their first meeting in the darkly comic Channel 4/Netflix hit, where Lawther’s character, James – a luckless teen with psychopathic traits – plots to murder Barden’s Alyssa. Slowly, the pair become more like Thelma and Louise, escaping retro-hued suburbia for increasingly high-stakes scrapes, from a carjacking to a run-in with a serial rapist. If this sounds heavy-going on paper, in reality it is a show that tackles difficult themes with a sardonic edginess and an often frantic pace that is in keeping with its comic-book origins.

Although neither Barden or Lawther are as nihilistic as their alter egos, there are some parallels: she is infinitely charming, a little spiky and restless, mockingly describing herself as “a degenerate”, while he has a more reflective, English-student vibe, an Extinction Rebellion badge pinned to the lapel of his coat. Really, though, they are a riot. They erupt into fits of giggles as they recount the story of how James’s house was knocked down in real life two days after the first season wrapped, with the character relocating to his car this season as a result of its demolition. “It’s such a James thing,” says Barden. “Charlie [Covell, the show’s writer] didn’t actually put that in the script because even she was like, that’s too much.” “My house has disappeared!” Lawther adds, fake-crying.

Ordinarily, the leads of a successful TV show would not be banished to the basement, especially not a show that – according to Netflix’s chief content officer Ted Sarandos – has been an “astounding” success for the streaming service, and which also broke records on All 4. But there is good reason for it: at the end of the first season, James was seemingly killed in a police chase. While fans will by now know about Lawther’s return – the second season dropped in one go on Monday – it was kept under wraps until the show’s transmission (promo posters featured Alyssa in a wedding dress, alongside an urn that many presumed contained James’s ashes).

Although the idea of killing James off proved largely unpopular with fans, a lot of theories swirled online prior to the show airing. “Some of them are amazing,” says Lawther, wide-eyed. “Alyssa being haunted by the ghost of James is an amazing idea. Another one was that it was Alyssa [who] was shot [by the police], and then season two becomes about them trying to break her out of jail.” Barden has been offering further curveballs in interviews. “People have been like: ‘Is James dead,’ and my answer is: ‘Am I dead?!’”

Adapted by actor Covell from Charles Forsman’s graphic novel and boosted by a Netflix deal that saw the series broadcast internationally, TEOTFW is not your usual teen show. As indebted to Tarantino as it is to Twin Peaks, its first season lunges from murderers to middle-aged perverts, attempted sexual assault to the awkward chemistry between two female police detectives, all punctuated by dark gags and an obscure, fittingly morose soundtrack curated by Blur’s Graham Coxon. The setting is a disorienting mix of British small-town-ness and Americana, via roadside diners and sprawling, overgrown forests. Although unconventional in many ways, it presents a classic conundrum: a tale of a will-they-won’t-they couple who are as good for each other as they are bad.

It is a mix that has proved hugely successful. As well as overshooting the broadcasters’ expectations, The End of the F***ing World has become one of those shows as likely to be dissected by teens on the internet as by heavyweight critics. It bridges the gap between Tumblr fandom and awards shows, having been nominated for both a Bafta and an Emmy.

While the pair admit that it is difficult to comprehend how big a phenomenon something is when you are actually in it, they know that hanging out in a shiny hotel bar would have given the game away. Barden has been spotted in places as obscure as a branch of Target in Ohio, while Lawther is often accosted in the street, although sometimes people get a bit confused. “I get people coming up to me and saying: ‘Ah, Asa Butterfield, I loved you in [Netflix series] Sex Education,’” he admits.

Facebook Twitter Pinterest New blood... Naomi Ackie as Bonnie (far right) with Karl Collins and Nadine Marshall. Photograph: Ben Spence/Channel 4

Lawther is not your average matinee idol: he looks far younger than his 24 years, is faultlessly polite and often uses interviews to get deep into subjects such as politics and why private schools should be abolished (he attended one himself, during a childhood in Hampshire which he previously described as a “middle-class bubble”). He is known for his outsider roles, including a teenage paedophile in Black Mirror’s Shut Up and Dance and a young, enigmatic Alan Turing in 2014 film The Imitation Game. Complex characters appeal to him – with James being a particularly knotty role to untangle.

“Initially, I thought [the show] was about a young man being violent towards a young woman, and I thought: ‘I’m not really that interested because there’s enough of that around.’ But I realised that James becomes something else. It’s not about his violence towards Alyssa, it’s about him understanding how he feels and working out that actually he’s not a psychopath, he’s just very, very, very sad.”

Barden, meanwhile, was born in North Yorkshire and landed a breakout role in Coronation Street at the age of 14, leading to parts in dramas and odd offbeat films such as Yorgos Lanthimos’s The Lobster. Alyssa wasn’t the kind of role she was used to playing but, says the 27-year-old, reclining on an office chair with more than a bit of her character’s forthrightness about her, it was a welcome challenge.

“At first it was just another part that I wanted to do, then it was: ‘Oh this is quite funny.’ As I got closer to when we actually filmed it, it turned into: ‘Nobody else [is] giving me an opportunity to do anything like this,’” she says. “At the time when we finally made it, I was continuously being told I would never be a lead in anything. I don’t fit the mould: I’m not trained, I have a working-class background and I didn’t want to do a grooming storyline or play a maid every time. I wanted to lead an interesting TV show. So in the end [this] was a complete breath of fresh air.”

She and Lawther met for the first time during the casting process in LA, on a trip that was equal amounts of work and play. “Our relationship started by being dry-iced in a nightclub and then suddenly feeling completely, instinctively safe with you when we couldn’t see anything for two minutes,” Barden explains. “You make people feel very safe on- and off-camera, and I think that’s how Alyssa and James make each other feel as well.”

Facebook Twitter Pinterest Natural bored killers... Barden and Lawther in season one. Photograph: Netflix

It is clearly something of an intense relationship, both on- and off-screen. What do its stars think of the idea, posited by critics and fans alike, that James and Alyssa’s might not be a healthy bond? “It’s an adolescent relationship where they’re exploring trauma and insecurity so it’s not really healthy, but it is a relationship that is present,” says Barden. “I think something only needs to be present to be healthy.” Lawther nods in agreement. “They fuck up a lot and do the wrong thing but it’s always with the intention of trying to help the other person or do the most loving thing,” he says. “Often they get it really wrong, but I don’t think it’s unhealthy to get it wrong.” Besides, adds Barden, “they might have been even more lost without each other.”

Up to this point, the show has been primarily about Alyssa and James, with the odd tangent to take in: characters such as police officers Eunice and Teri and their sexual tension, or would-be rebel Frodo – a fan favourite played by Nick Cave’s son Earl, who helped the pair to hold up the service station where he worked, before realising there was only room for two on their getaway mission. This time, though, their story is neatly interwoven with that of Bonnie, another outsider with a bone-dry sense of humour, who – in a trademark curveball – is the subject of the entire first episode.

Bonnie is played by Naomi Ackie, a future household name who has a role in the upcoming Star Wars film The Rise of Skywalker. Rather than interfere with the double-act chemistry, Ackie proved an ideal addition to proceedings; seeing her on set with Barden “really solidified what we were making”, says Lawther.

The pair also bonded with Tim Key – who plays another new character, unnerving motel owner Gus – even if Barden visibly cringes when recalling their first day together on set. “Obviously somewhere in my brain, I was like, this guy is in Alan Partridge, but it didn’t connect, so I was going around shouting ‘A-ha’. When I realised, I was like: ‘I look like such an idiot!’”

As well as Bonnie and Gus’s stories, we also get a James-free look at what Alyssa’s life has been like in the time since that fateful police chase, including the reason behind what Lawther jokingly describes as “that fuck-off big dress”. Did they ever imagine a world where the show might have abandoned James altogether? Barden claims she always knew they’d be back together. “It just wouldn’t work,” she says firmly. “The show is Alyssa and James together, you know – that’s what it is.” Besides, she adds with a mischievous glance at Lawther, “people would have been so annoyed with us.”