In a lovelier, livelier version of our world, Mr & Mrs would be prime-time viewing, but with one vital tweak: the only contestants would be Edwyn Collins and Grace Maxwell. Inclined towards bouts of raucous laughter, the singer-songwriter and his wife speak in lovely intertwining sentences, their words like batons to be passed ever forward, firm evidence of some 30 years spent in one another's company.

“I’m from mad, industrial Lanarkshire,” Maxwell says.

“And I’m from Edinburgh,” Collins says in plummiest Burgher before they collapse into giggles.

They talk fluent couplese. “Oh, tell her that story,” or, “We have very different types of brains, haven’t we?” or, “No, no, that one.”

“Back when we were in a wee one-bedroom flat I decided I wanted to sound professional, like I was working in an office or something,” Maxwell says. “So how did I used to answer the phone, Edwyn?”

He stops laughing to affect a sing-song telephone manner: “Grace Maxwell.”

“He used to mock me for this relentlessly,” Maxwell says. “And, just to add to his fun, Edwyn used to pretend to be my assistant.” She drops into a standard bureaucratic mockney accent: “I’m not really authorised to make these decisions.”

Maxwell has a theory that this comic parroting was lodged in Collins's brain when hardly anything else remained. In 2005, Collins, former frontman of the wildly influential Scottish band Orange Juice and the solo singer behind the global 1994 smash A Girl Like You, suffered a huge cerebral haemorrhage. A second, near-fatal stroke followed within days.

“I was taking a meal just before my stroke,” Collins says. “It was a Sunday. And I thought the potatoes tasted a bit burnt. And something rushed over me. I was asked, ‘Are you all right?’ And I didn’t know. I couldn’t move.”

He still requires patience and space to finish certain sentences. He takes care enunciating words such as “mesmerising” and “vulnerability”. But it has taken nine years to get here. Today I’m chuffed that he uses my name a lot – this must require an effort on his part. His recovery process has comprised tiny, incremental steps: learning to draw birds with his left hand when he used to be right handed, learning to read again from Ladybird books, learning to hold down chords while Maxwell strums.

This process is chronicled in a gorgeous new film, The Possibilities Are Endless, from the hotly tipped young directors Edward Lovelace and James Hall. The title comes from Collins's initial months in intensive care, a time when his only words were "yes", "no", "Grace Maxwell" and "the possibilities are endless". The latter, Maxwell says, stops sounding in any way poetic when you hear it 100 times a day.

“The doctor would visit and say, ‘How are you this morning?’ and Edwyn would say, ‘Grace Maxwell. Oh, eh, Grace Maxwell. Oh God, Grace Maxwell.’ There were, in my mind, always signs that he was still in there. But for a while he didn’t seem to know who he was.”

He recognised Maxwell and their son, Will, who appears in the dreamlike film as a younger Collins. But details such as his career and his music were lost at first.

“I remember I was very mad,” Collins says. “And it can still be frustrating as f***.”

“He would get stuck for ages,” Maxwell says. “Sometimes we would just have to give up. We had to learn to just let this one fly away. But that doesn’t happen any more. Because now I can read his mind.”

The Possibilities Are Endless opens with footage of Collins's appearance on Late Night With Conan O'Brien in the mid 1990s, when he could look back on a career that saw the foundation of the hip Postcard Records imprint and an Ivor Novello award. Mostly, however, the film-makers have eschewed archive footage – "a bit too Spandau Ballet", apparently – in favour of Collins's own, initially jumbled recollections.

His damaged neural pathways make for something like interrupted beat poetry, playing over scenes shot in and around the couple’s rural retreat at home at Helmsdale, Sutherland.

“Edward and James created this weird, very quiet atmosphere in the studio,” Maxwell says. “I was banned because we’re quite a shouty house. And I’d have brought that with me. Edwyn isn’t quiet at home. But in a public setting, when there are lots of voices and lots of people, he finds his aphasia” – difficulty understanding and expressing language – “is a good bit worse.”

For the opening half-hour of the film Collins is audibly striving for meaning. He doesn’t enjoy watching that section, according to Maxwell.

“I was maybe very nervous at first,” he says. “We were recording me talking for two years in the studio. It’s terrible at the beginning. It’s me stuttering and not making sense. But it wasn’t up to me. The guys knew what they were doing. The viewpoint is true to life. The connections are loose.”

They’re loose, but not consistently so. He can remember a great deal of his childhood in Edinburgh. “But if I remind him about some weird hotel that we stayed in on tour in Austria that mightn’t be there at all,” Maxwell says. “He remembers the fun stuff sometimes. But he could always discard things. I call him the man who hasn’t paid a phone bill since 1982.”

He calls his life before the stroke his "premorbid life", but in his post-premorbid life he has bounced back to produce three solo albums: Home Again (2007), Losing Sleep (2010) and Understated (2013). For the moment, however, the couple are locked into a promotional tour for the film.

“It’s a wonderful film, fantastic,” Collins says. “It’s not really ours,” Maxwell adds. “But in a good way. Because we still get lots of credit.”

Maxwell suggests that Collins is a kinder, gentler person since the illness. He’s not so sure. “I have some difficulty with my speech, but I’m certainly the same person inside.”

Maxwell turns to him. “But in the power struggle of our marriage the younger Edwyn would never have put up with how things are now. That’s the problem with the situation. It creates an imbalance of power. As he has got stronger it’s a bit more like it used to be. He’s harder to control. But I feel terrible sometimes, because I end up ordering everybody about. It has turned me into Margaret Thatcher.”

“Tell me about it,” he says. “Call social services.”

The imbalance isn’t too pronounced. Maxwell would like to give up their Kilburn residence in order to relocate to Scotland permanently.

“I just want to sit by my fire in Helmsdale with my feet up,” she says. “I’m at an advanced stage in life. I just want a fire and a wee sherry.”

“And I’m not going to let you,” says Collins.

And they laugh like they always do.

The Possibilities Are Endless is at the Irish Film Institute

Postcards from the past: five essential singles
Postcard Records, founded by Edwyn Collins and Alan Horne, released a little over a dozen records in its initial incarnation. In the early 1980s, NME readers held the Glaswegian record company in equal esteem to Factory or Rough Trade. Collins's Orange Juice and Roddy Frame's Aztec Camera (above) went on to mainstream success. The more abrasive Josef K are one of the great underappreciated bands of the era. All combined blue-eyed soul with Velvet Underground jangle to hugely influential effect. Here are five key singles.

I Need Two Heads
By The Go-Betweens (1980). The Australians were suitable fellow travellers.

Just Like Gold
By Aztec Camera (1981). The most plainly melodic of the Postcard bands.

Falling and Laughing
By Orange Juice (1980). Edwyn Collins's (and his label's) first release.

It's Kinda Funny
By Josef K (1980). Still the sound of an era for about 125 obsessed fans.

Simply Thrilled Honey
By Orange Juice (1980). The breathy camp comes together triumphantly.