Light relief: How the volatile actor Paddy Considine came to terms with an unusual ailment

Paddy Considine was renowned for being as intense, edgy and taciturn as the characters he played. Until, that is, he discovered he had been suffering from an unusual syndrome for two decades that drove him to the point of destruction.

The Kelvin Amateur Boxing Club has seen better days. There's graffiti on the walls, bare brickwork, shot plaster, the ticklish smell of fresh sweat, the tang of three decades of Scottish testosterone.

Outside, it's December 2011, and frigid rain is falling on Glasgow. Inside, it's week four of the six-week shoot of an independent British film called Honour. The subject matter – honour killings within the British Muslim community – has already made raising the budget for the film a drawn-out affair. According to producer Nisha Parti, "lots" of financiers rejected the project "because they felt it was a bit controversial. And the fact that it was really a cast of brown people, which is never easy to market."

The only white person – and the only "name" actor – within the core cast prowls the boxing-club floor. Paddy Considine is gloved, sweating, tattooed with a spider's web on his elbow, bandaged on his forearm where another inking – the words "Aryan Brotherhood" – has been crudely burnt off. He's in character as a racist, nameless bounty hunter hired by a Pashtun family to track down and murder their errant daughter, who has brought shame on the family by dating a Punjabi.

Shan Khan watches admiringly. "When he hits a bag, it stays hit," says the London-born, Lanarkshire-raised screenwriter and director who is making his feature debut with Honour. "Most of our actors are metrosexual boys. They need to man up." But Paddy, he states firmly, is a man with gravitas.

Considine punches the bag hard for 105 punishing seconds. He does this through five takes, sweat pouring off him. The actor has great comic chops, as displayed in Edgar Wright and Simon Pegg's Hot Fuzz and Richard Ayoade's Submarine. But he's better known for dark roles in dark projects such as Shane Meadows' Dead Man's Shoes and Channel 4's Red Riding. Honour falls squarely into the latter camp, another intense role for an intense man. Between takes, Considine stays separate on the crowded film set, muttering to himself, singing absent-mindedly, his eyes staring, flitting and blinking in the bright lighting.

"It's been pretty lively," is his terse summation of the shoot so far. Khan relates that his leading man had complained to the director that too many of his other roles "spazz [me] up". But as written in the Honour script, his character speaks in a choppy, taciturn manner. "That's my territory," acknowledges Considine flatly. "Not big fucking monologues."

I'd last seen him only three months earlier. I interviewed him and Peter Mullan prior to the release of Tyrannosaur. Considine's directorial debut was a harrowing account of domestic abuse, fractured families and wrenchingly lonely people, with the Scottish actor in the lead role. We'd had a great three-way conversation, with Considine relaxed as he discussed the Asperger's with which he'd recently been diagnosed. He was even able to joke about one aspect of the condition: his current obsession for stripes, hence the striped sweater he was wearing.

The film had had mostly brilliant reviews, and won various awards, including a World Cinema directing prize for Considine at the Sundance Film Festival. But in Glasgow, he is narkily focusing on one comment: a reviewer had remarked that the film, scripted by the Staffordshire-born father-of-three and loosely autobiographical, was "poverty porn".

"I wanted to punch the cunt in the face for that," Paddy Considine states, boxing gloved-hands at the ready, eyes staring at me. I don't doubt him for a second.

"Oh, I really love Boy George!" Considine says brightly. It is late March 2013, and we are talking in a meeting-room at ITV in London. I have just told the actor/writer/director of a recent work assignment involving the 1980s pop survivor. "They're all shaping up well, those guys," he beams. "I'm a big Adam Ant fan. He's looking in great shape. He's just released this record, I love it."

This is surprising stuff. Not the passion about music. Considine can happily prattle on for hours about his favourite group, cult US alternative-rock outfit Guided By Voices. Plus, he's long been in bands himself. He first met Shane Meadows – the director who turned him into an actor by casting his untrained, unsuspecting friend in A Room for Romeo Brass (1999) – at Burton College in 1990. Both were studying for a National Diploma in Performing Arts course, and neither completed their studies. They bonded by playing music – and acting the goat – together. Twenty years on, Considine maintains a healthy extra-curricular passion, singing and gigging with a band called Riding the Low. Their debut album is due out this summer.

So it's not so much the interest in the music as much as Considine's demeanour that's surprising. He is, well, sunny. Light, amiable, relaxed. Even when he I met him as he and Meadows promoted 2009's mock-rockumentary Le Donk & Scor-zay-zee – Considine played a mulleted Arctic Monkeys roadie – he wasn't this chilled.

Is he buzzing because he has two interesting projects coming out within weeks of each other? Honour is due out later this year, and before that the actor returns in the title role of The Suspicions of Mr Whicher II, a follow-up to the highly rated ITV drama about a Victorian murder mystery.

"I'm just in a different place, personally," he states. Since his Asperger's was diagnosed, "it's been quite a journey, Craig," he says, the first of eight times he will use my name in the course of our conversation. "There's been a lot of ups and downs, but really big discoveries as well. Things that have enabled me to get well and feel much better."

I ask him to break down what was wrong. "For years I haven't been well," he replies. "And also, I had no idea really how to act. I realised that I had no tools for the job. There was no apprenticeship."

In empirical terms, this is true: his college mate Meadows, keen to work with raw, untutored talent, cast him in his early low-budget Midlands-set capers. And that was it: Considine's career had stuttering lift-off. He was, as was often claimed, Britain's Robert De Niro. He'd occasionally pop up in big-budget films – Cinderella Man (2005), The Bourne Ultimatum (2007) – but mainly he maintained a cool profile as an "edgy" actor in "edgy" projects, an enigma who refused to audition, was picky about projects, and maintained a prickly reputation.

"I always loved acting – I always felt there was some ability there. But I realised in interviews [that] it came off like I was hating it."

Again, this is true. I first met Considine in 2005, in northern Spain. He was making a film with Gary Oldman, and I went there to interview him about Cinderella Man. He wasn't wild about the part he had in the latter, a Depression-era true-life yarn about a boxer starring Russell Crowe. And he wasn't too keen on the former either, even though it was a chance to work with Oldman, one of his heroes. Later that night, after we'd sunk multiple beers in his hotel, he let me kip on his bedroom floor, but not before telling me ear-curling yarns about his working-class upbringing in Burton-on-Trent (where he still lives). Six years later, I recognised some of these tales in the bleak, brutal Tyrannosaur.

"I couldn't engage with acting," he continues now, his fingers flexing and unflexing. "If I was improvising, I could access that my part of my brain. If I was working with Shane, I could give him all these [performances]. But when I was given a written page of acting, I couldn't get beyond it. It led to people saying, 'An incredibly restrained performance by Considine.' I thought I looked fearful, afraid to do anything."

It all fed into a sense of promise unfulfilled. For all the critical acclaim, Considine never had that break-out role. People close to him could see it was more than bad casting, or bad attitude. He'd felt "disengaged from everything" for years. His wife Shelley – they met when he was 18 – did some research, and suggested her husband see a specialist. In 2010, he was diagnosed with Asperger's syndrome. It didn't bring relief.

"My ability to be in a room with people was getting worse. My ability to socialise, to make contact. I was basically closing down."

Considine went to see a Harley Street psychologist, who conducted some tests. His opinion: the actor was suffering from a severe case of Irlen Syndrome. According to the website of Irlen UK, this is a condition whereby the brain "is unable to process full spectral light… This results in a range of distortions in the environment [and] on the printed page, [and] physical and behavioural symptoms. It is exacerbated by environmental factors such as lighting, brightness, glare, high contrast, patterns and colours."

Does that mean the room in which we're currently sat – big windows, bright red coverings on chairs, a low-hanging bulb, reflective surfaces, shiny green bottles on the table – is a nightmare?

"Well, I'd be looking at you now and the wall would disappear. Your face would disappear. The light off that glass would be hitting my face and all the time we're sitting here, I would feel like getting that bottle and hitting you with it."

As he's been talking, Paddy Considine has been poking at his eyes and rubbing the edges of the sockets. Now I know why: he's wearing tinted contact lenses to filter out the light. Previously, he says, he had an ever-present "knot at the back of my head". Now, he smiles, "I can look at you, my brain is settled, and I'm well." And he's been suffering like this for how long? "Twenty years. Driving me to the point of destruction." No wonder the Considine of old was so tense.

Simon Pegg, his Hot Fuzz collaborator, had a close-up view of the change. Late last year, he and Edgar Wright worked again with the actor, having cast him in their new comedy, The World's End. Considine's Irlen lenses arrived midway through the shoot. "We could all see Paddy was suffering a little bit," recounts Pegg. "He was having to deal with the condition and also focus on acting. It's like juggling 20 balls… Once they'd arrived, it was amazing – he just relaxed. There's an edginess to Paddy which is necessary for who he is, and it's hysterical and brilliant, and it empowers him. It just took away the negative aspect of that edginess."

Similarly, we can now view Considine's career with "before" and "after" clarity. Honour is a decidedly "before" project. The film's brutal subject matter is gripping, although the back-and-forth timeline is confused. It's a situation not helped by, yes, another incredibly restrained Considine performance.

Filmed earlier this year, meanwhile, The Suspicions of Mr Whicher II is his first fully post-Irlen project. The feature-length drama sees Considine reprise the character of the titular detective in a new, specially written investigative story. "I felt like I was better at interacting with people," he reflects of the making of Whicher II. "I was giving more and getting more back."

It's traditional Sunday-night TV, a drama that ticks the voguish historical/period boxes (see: Downton Abbey, Whitechapel, Ripper Street), and hopes are high that it will be commissioned into a series. The "old" Paddy would have turned up his nose at such mainstream fare, and the prospect of committing to a recurring role. The new Paddy is more pragmatic: "Not many people give you a lead role and ask you to come back."

Considine is looking ahead in other ways, too: this year he is hoping to shoot his second directorial project, an adaptation he's written of a book called The Years of the Locust, an account of an American boxing scandal in the 1990s. What happened to the plan he told me about in 2011, that his next film would be a ghost story he'd written? "I've parked it. It didn't mean anything. It was just a dark ghost story." And Paddy Considine, hitherto blinded by the light, has had enough darkness. Good for him.

'The Suspicions of Mr Whicher II' airs on ITV later this month. 'Honour' (15) will be released later this year