If you've laughed at a British television show in the past 15 years, you'll recognise Matthew Holness.

After a series-stealing cameo as Simon the IT guy in The Office ("Oi, no professionals"), Holness found belated success after writing and starring in surreal 2000s comedy Garth Marenghi’s Darkplace – a tongue-in-cheek paranormal caper set in a Romford hospital, wherein the protagonist, Rick Dagless, accidentally opens a portal to hell.

Starring himself, alongside a young Richard Ayoade and a cherub-faced Matt Berry, Darkplace drew underwhelming viewing figures initially but became a cult classic on DVD (and has almost certainly since been recommended to you by a guy with a ponytail at a party). A later spin-off series, Man to Man with Dean Learner, helped to launch Ayoade's career, but Holness' participation in comedy started to fade. And while he was away, he was out there getting spooky.

Possum, Holness' directorial debut, could scarcely represent a sharper detour from his early work. The film charts a troubling journey into the mind of Phillip, a Jimmy Savile-inspired disgraced puppeteer played by a squirming, sinewy Sean Harris. Carrying a puppet in a brown satchel, Phillip returns to his grotty childhood home to be greeted by Maurice, his rasping, obnoxious uncle, played by Alun Armstrong.

Phillip's attempts to destroy this horrific puppet – composed of a blank, expressionless human head attached to spider's legs – prove fruitless as he explores a grim and desolate Norfolk. All the while, reports of a missing schoolboy echo out through TV static. Rich in symbolism but sparse in dialogue, Possum is a haunting and otherworldly exploration of Phillip's psyche as he struggles to shed the trauma of childhood abuse.

The journey from cult comedy to intense psychological horror hasn't been easy for Holness: "I've always wanted to do serious stuff, transition from comedy into more serious filmmaking," he explains. "Trying to convince people that I want to make a serious film about very dark themes – they kind of say, 'Why don't we do a comedy? It will be more money and we'll get more audiences in.' It’s been difficult, really."

Sean Harris in 'Possum'

Since his delayed recognition in Darkplace, Holness has featured in a smattering of other sitcoms and comedy TV shows, without hitting the same 8 Out of 10 Cats recognition status as many of his contemporaries. His passion for horror was evident as we chatted over the phone, making it easier to understand why he's leaving comedy behind, at least for now. "I find writing comedy very hard; it's a lot of headwork, it's very technical," he says. "Whereas writing something like Possum didn’t feel like that. Writing horror is much easier; it flows more and feels more natural."

Possum began life as a short story, as part of The New Uncanny, a collection released by Manchester-based independent publisher Comma Press back in 2008. Based on Freud’s work attempting to understand the essential human fears, Holness produced Possum as a culmination of his own personal phobias of dummies and doubles, creating a puppet that served as a grizzly self portrait of its owner; a symbol of a deeply-troubled past.

Despite the glaring differences between his early and recent output, Holness sees similarities between comedy and horror as art forms: "They share something in expressing something that we usually couldn't express, tapping into people’s subconscious and sense of unease, or embarrassment, or whatever it is," he explains. "There's something similar in tapping into things that people wouldn't normally want to talk about."

Sean Harris in 'Possum'

This exploration of the unsayable is also reflected in the 1970s-inspired aesthetic of the film – a previously innocent era that has now come to be recognised for its horrendous abuses of power and subsequent cover-ups. "It's not because I think the 70s are a wonderful period, because it would appear they were anything but," says Holness. "It fitted the story to have [Phillip's] reality reflect a psychological state that he'd never left, so he was still at the stage of this trauma – he's still in the 70s in his head, he's not moved on. I didn't want it to feel nostalgic in any way."

Holness explained that a key inspiration for Possum’s visual style also came from the public information films of his youth, government-commissioned shorts intended to shock young people out of making dangerous decisions, often depicting children being maimed, killed or kidnapped after sneaking into power stations or accepting gifts from strange men.

"They were put on between children’s programming during the day; you’d see these horrific, terrifying films – you got the impression that the adult world was a very tribal place," he says. Ironically, some of these safety films featured voiceovers from now disgraced celebrities, one of whom was Jimmy Savile. "Of course, now we know several of those films are fronted by real-life monsters," adds Holness.

This 1970s atmosphere is also evident in the tinnitus-inducing shrieks and warbling bass of Possum’s soundtrack, which was produced by the BBC Radiophonic Workshop, a studio responsible for much of the audible output of the period. "The Radiophonic Workshop became so powerful to me, as they were the background to those programmes," says Holness. "They were really reassuring in those days, producing music for programmes like Doctor Who. It was the sound wallpaper that Phillip would have had in his head."

Music plays a considerable role due to the sparse script, scoring Phillip's attempts to burn, drown or destroy the physical manifestation of his trauma, to no avail. Much of the dialogue is restricted to Maurice berating a clearly terrified Phillip through nicotine-stained teeth, or abuse shouted at Phillip from strangers in the street. It's telling that Possum was originally intended to be devoid of dialogue altogether, with Holness taking inspiration from classic silent horror films like Nosferatu. "I'd been watching a lot of old silent horror films, German horror films, existential horror films, and I was thinking, 'Would it be possible to make a modern silent horror film?'" he says. "I was looking around and thought I had a story where someone had suffered trauma and couldn't talk to anyone."

Whether it's a fear of dogs, heights or spiders, childhood is when the majority of irrational fears and phobias take hold. Holness intentionally references these formative years by punctuating the film with intensely creepy fairy tale-esque rhymes: Here’s a bag, now what’s inside, does he seek, or does he hide? Can you spy him, deep within? Little possum, black as sin.

Alun Armstrong in 'Possum'

Each verse is read aloud by Phillip from a scrapbook inscribed with disturbing charcoal illustrations, like the world's creepiest children's book. Fairytales and folklore form the foundations of a staggering number of contemporary monsters – with even internet-age horror meme Slender Man having its origin rooted in the legend of The Pied Piper of Hamelin – and Possum is similarly rooted in horror lore. "Particularly because this was a story about a child abduction," Holness explains, "a way to do that sensitively and make it palatable in a horror film is to do it the way the Grimm fairy tales would cover it."

"There's something distinctly creepy about using a children's fairytale story to reel the audience in: it takes you back to that primal stage, those early years when we're slowly starting to encounter the adult world. We're warned at an early stage in a way that’s acceptable for a child. It’s how we learn about what to be afraid of, what to be careful of."

Whether it’s the tentacular legs of Phillip's puppet or thick black smoke engulfing a bunch of yellow balloons, symbolism and allegory are rife in Possum. "I think most monsters or ghosts are all representative of something else. In the best ghost stories, they aren’t about creatures from beyond the grave," says Holness. "For me, the best ghost stories could be that, or could be a manifestation of the inner workings of someone's psyche. The guilt, the trauma, or whatever the character is repressing in their mind, comes out as a ghost of some kind."

It's clear from movies like Possum, The Babadook and It Follows that horror is a genre ideally suited to exploring serious subjects, rather than the jump scares, exploitation and gore that has come to define much of the genre. Holness also passionately believes that horror movies have a responsibility to tackle weightier themes.

"All the great periods of horror films coming out have all coincided with world events and times where there's been a lot of unease and anxiety about world affairs," he says. "They do have a duty to confront things that people aren't saying or shying away from, that people don’t want to admit. I feel like there will – and should – be some quite unpleasant horror films coming out."