A nice man is telling me a story. He was once what used to be known as a rock star, and he is telling me a little story, about a drunk woman who had accosted him in a friendly way, just 48 hours previously, in West Hampstead. She lurched down the street, eyes on our man, and trilled out: “I never met a girl like you before!”

The first noteworthy thing in the telling of this is that the teller is Edwyn Collins. Edwyn was once frontman for celebrated Scots indie band Orange Juice, and was later to carve out a solo career (which included the global 1994 hit “A Girl Like You” hence, two decades later, drunken recognition on the mean streets of West Hampstead): a Novello winner, a noted producer, a sought-after collaborator. In February 2005, two days after complaining of feeling unwell, Edwyn suffered a cerebral haemorrhage and was rushed to intensive care in London’s Royal Free hospital. Days later, he suffered another. They were both on a catastrophic scale, and his wife Grace was told to, basically, stock up on the Kleenex and await the worst.

Which is why it’s rather lovely and a little miraculous that Edwyn’s here, in his Kilburn home, to be able to tell the story. He does so in an exceedingly halting fashion. There is much stuttering, still. His wife, Grace Maxwell, and I strive not to fill in the next words for him, as one should so strive, though in Grace’s case that must take superhuman effort, still: a voluble Bellshill lass, she could talk every available limb off a donkey. So, all in all, this small story takes about three minutes to tell. But the remarkable thing is this: when he gets to the nub, the 50-year-old woman singing out, he takes the lyric in swooping stride, arcing down the scale to the old splendid baritone, not a flicker of a stutter. He tells me later that he finds it much easier singing than speaking, and much simpler drawing than writing.

And these and the many other unfathomable mysteries, anguishes and delights of the synapses and neural pathways of the human brain are now explored in a film about Edwyn’s story – told, haltingly, by Edwyn himself, and shot through with lingering footage of his and Grace’s beloved Helmsdale, in Sutherland, to which they’re moving permanently in a matter of days now.

The new film,The Possibilities are Endless – the reference is to one of the few phrases Edwyn could manage during his long early months in hospital – premieres at the London Film Festival on 11 October and has already been nominated for best documentary. It is a slow delight. The word “elegiac” will surely be used. In terms of action and pace it is not, I venture to Edwyn, exactly Terminator II, and I am rewarded with the first of his many huge laughs, a warm, gurgling bark. But what it is is a little bit of beautiful.

Young filmmakers Edward Lovelace and James Hall have helped tell Edwyn’s story with immense grace: there are very long shots, resembling stills in their intensity and framing, of a just-moving stag, say, or a wash of colour from gorse you can almost smell. I felt that I was watching a simple understated celebration of the sheer joy of living, the taking of uncomplicated pleasure in every fresh dawn.

Grace, from her comfy position on the floor pouring coffee, grows unaccustomedly quiet as she looks across to Edwyn. “Yes,” she muses. “You’ve said it for nine years now. Over and over again. Edwyn goes – it just hits him, he’s overwhelmed by it – and he just goes: ‘Oh God, how glad I am that I’m alive. And how close to… not being here.’”

“You mean,” Edwyn interjects, “to death.” Huge bark of laughter.

We talk about the months after the stroke, and Grace prompts Edwyn to tell me how it was. He looks me directly in the eye. “Well, terrible! I couldn’t talk, couldn’t communicate, no language. The words I could say were ‘yes’ and ‘no’, and ‘the possibilities are endless’. I had to learn to read again through… Lady… Ladybird books.”

Grace adds: “He would get stuck on a phrase. For a while it was – ‘the situation is… the situation is’. And then, suddenly: ‘The possibilities are endless.’ No one’s quite sure where it came from. See, Edwyn could sometimes repeat things. The doctor would come and say: ‘Hello Edwyn’ and he could manage a hello. Then the doctor would ask: ‘How are you feeling today?’ and Edwyn’d just go: ‘Ah. Ah. Um… Grace Maxwell, Grace Maxwell.’ He barely knew who he was.”

“But I knew I was Edwyn,” says Edwyn. “I knew that was me. I knew Grace, and my son.” But, I ask, who “was” Edwyn? “Me. I knew that, and that was important. I was Edwyn, as opposed to… Euan.”

Did you know you had been a musician? “Hmm – yes, I did. But they were very bad months. I would have a thought and try to pin it down. But it would… evaporate.”

It takes him a good time to say this word but he perseveres. “To help me, I used a book. I still do.” The book is one of the banes of Grace’s life: she’s tried to buy him a new notebook, but he insists on the old, knows every twitch and scribble of it. Nine years of phrases and words, scrawled and rescrawled every which way, all done with the left (wrong) hand. It tells the slow jumble of a brain regaining.

But what saved him, a good bit, was drawing. Grace again: “The stroke was in February, and he came back home in August. By November I’d persuaded him to try to draw a bird.” Edwyn, born in Edinburgh, moved when young with the family to Dundee, where his father had been appointed a lecturer at Duncan of Jordanstone College of Art and Design. At about 20, just before he formed Orange Juice, he had a job as a graphic artist for Glasgow’s parks department.

“So,” says Edwyn, “I thought I could try to draw a wigeon. A female duck. Quite crude, but I was happy. I called out: ‘Grace, come and look at my drawing!’” His wife – and long-term manager – says: “That was really important. Ten months after your stroke you discovered something which it was apparent immediately you were going to get better and better at. Edwyn wasn’t back to music at all then, and we didn’t know at all if he ever would be.” Edwyn has since exhibited his wildlife, and rather damned good it is.

“It is something like therapy for me. My brain relaxes when I draw, and can see the pages unfolding. And” – Grace is trying to interrupt but he fends her off with adeptness and a warm smile – “I must explain something to Euan. Before my stroke. My drawing. Was taking me ages to do it. For example a wigeon, but… one week to do! But after my stroke, I became free. As a bird! I came terribly relaxed, and I’m working on things, a quick sketch, and it’s much better than the ‘artiste’ stuff I did before the stroke – I became much freer.”

Grace is allowed to speak, eventually. “You did. In many ways. And there are new things, such as a wave of emotion can move you to tears. You have, I have to say, become so much more tender hearted.”

As opposed to what? “Oh, Edwyn was lovely, but opinionated.” Her husband agrees. “I was. Admittedly I used to express myself better – but I was a…”

“A show-off?” beams Grace, and he stills her with a glance laced with irony and self-knowledge. “I was an innate intellectual, actually.”

“He was a journalist’s delight. He used to say exactly what he felt.”

Then, slowly, the music started to return. Edwyn can’t, thanks to the right hand, strum any more, but he does manage mean chords. He limps up and across to fetch a guitar and shows me how the simple placing of fingers on frets can be made to work, especially if amped up. “I use an amplifier on it, hammer away chords on the left hand, and it works. Mainly the Memphis chords. Steve Cropper, Otis Redding, those guys. Plus, I’m surrounded by great people.”

He has toured, to acclaim, though critics have occasionally found the need to contrast the singing with the quality of speech between numbers, and is eager to tour again, and often. He performed, with his 24-year-old son James, when the film had its international debut at the South By Southwest Film Festival in Austin, Texas.

And so they’re moving kitchen sinks to lovely Helmsdale. Grace has already organised – and no small feat, this – the moving of his studio in West Hampstead to Sutherland: Edwyn has a family croft there, the legacy of a beloved grandfather, but they’re also having a brand-new studio built nearby. One question is: why, after all this time? They are undeniably and happily Scottish – they both voted yes in the referendum, though each says it was a conclusion reached after much thought, neither being a natural Nat – but: after all this time in London?

Grace, says Edwyn drily, is “too angry for London. She relaxes up there.”

“I’m not too angry,” she chides back, “but happy to admit the permanent move has been driven by me. Because it’s beautiful, and I’m from industrial Lanarkshire. And I’m now 56, and I resent that we have that place, are part of that place now, and we’re not there. I never feel the other way round. And these years since your stroke have been nothing but adventure, really: breakthroughs, new things, so many firsts – but it’s pummelled me a wee bit.” Edwyn is rocking with quiet, contained laughter.

The film has Grace asking, a couple of times, tenderly and rhetorically: “Who deserves this? Who really deserves this much beauty?” It also features much of Edwyn’s voice – a doubtless time-heavy process. “Ed and James would take Edwyn to the control room, and stick the tape on, and just stay quiet,” says Grace, and Edwyn adds: “Grace. Stayed away. That’s important. She had a quick listen at the door. A nosey, in fact. But it was politely conveyed to her that it might be better if she absented herself.”

Grace, lovely Grace, is keen to get in again. “You said to me, Edwyn, you said: ‘They don’t talk over me, like you do; they don’t coax, they don’t interrupt.’” A smile flits over his face. “Yeeees. And the first interview I did, I was hesitant. But after a while I became more relaxed. Stammering is a problem to me. But they didn’t interrupt, just let me talk. They put me in a good place.”

Stammering apart, does he still find problems with speech? “Oh yes. I still get the hesitantness… creeping up on me, of course. It’s tedious. It’s frustrating. But also what annoys is getting wrong the precise meaning, the precise words, the attitude meant to be conveyed by the sentence. I just think afterwards: ‘That would have been a better word.’

“But the film – well, I just let them get on with it. I’ve never been a fan of too many cooks. With music, too, I would… the record labels had too many cooks and sticky fingers. I grew to not like people breathing down my neck. So we just let them make the film, and then we saw it – you just have to trust them completely. And it turns out that it’s a… lovely film.”

We talk a little about Scotland again and they tell me a related story of Murrayfield, the national rugby stadium, where Edwyn’s grandfather had incidentally been capped, and where recently the authorities refurbished the entire pitch, allowing fans to take the old turf. A friend tweeted to Edwyn something along the lines of: “They’re playing your song.” Right enough, ‘Rip It Up (And Start Again)’, the big Orange Juice hit, was belting out on the Tannoy.

I’d always semi-wondered: what was the song about? End of a relationship? A life, a job?

“Not so much. Um… what was it about? God, I can’t remember. It was basically a bass line. I did the line on a Roland 303 keyboard. It was a good line, and I rather concocted the lyrics around it. Much of the rhythm guitar was ripped off from Chic. I ripped the lead guitar line off the Buzzcocks, but as a happy acknowledgment – I loved them.”

So, by rights, I suggest, it should have been called “Rip It Off (And Start Again)”? Edwyn howls with laughter.

I had been a little anxious, pre-interview, about how bad Edwyn’s memory loss was: total, sporadic, or recoverable? Accounts varied. Turned out it was pretty much perfect. I had brought a letter my friend Alastair had asked me to take to Edwyn. Since I had the misfortune of being mildly buggered by a stroke of my own last April, Al, once my co-sax player in a Dundee soul band in the 80s, has become a powerful old friend.

Grace looks at the name on the letter. “You remember Alastair – he sent you things in hospital, he wrote to you in hospital. You’re very rubbish about keeping in touch with people.”

“Oh, Ally Derrick, of course. I was once in a band with him. Called Onyx. Teenagers. Dreadful.” What did Alastair play, could he remember? “He played ukulele. It was really inappropriate in a heavy-metal band. I really liked him.” He wheezes with laughter, basking in the delightful lack of an absence of memory. Did he ever feel, with the musicians, and the touring, that any individuals had ever taken slight pity on him?

He replies with a certain obliqueness. “The first album I came back with, the lyrics are kind of direct, some would say simple, language: ‘Losing sleep, I’m losing sleep, I’m losing dignity, everything I know is right in front of me, and it’s getting me down’.” Again, he sings the lyrics with great and surprising fluency. “But the new album, Understated, I’m playing with the words again.”

It’s up to Grace to help out. Splendid Grace, with her deep love of, and understanding for, this man: and it’s so obviously mutual that I am near-unbound. “What Euan really means is do you think anyone’s ever patronised you? After the stroke? And I can answer that. You didn’t really care about that, did you? About what other people’s thought processes are or what demands he’s making on them. He’s just this bloody gigantic ego. Still.”

I walk from the door in Kilburn but can still hear his laughter in its bubbling glory.

The Possibilities are Endless will preview in cinemas and on iTunes from 20 October before its general UK release on 7 November (thepossibilities.co.uk)

Win a free pair of tickets to see Edwyn Collins at the Observer Ideas Festival. Our event on Sunday 12 October is at the Barbican in London and features scientists, chefs, musicians, mathematicians, artists and more for a day of inspiring talks and performances. Tickets cost £75 (observer.co.uk/observer-ideas or call 0330 333 6898). To win a free pair of tickets, go to observer.co.uk/win-ideas-tickets