In 2009, Edwyn Collins sat down opposite me in the BBC Scotland’s green room at the Glasgow leg of the Children in Need appeal. The singer and producer was slowly returning to public life after a life-threatening stroke and we spoke for ten minutes; but his pleasure in performing was mixed with an obvious frustration at his ability to communicate offstage.

Five years later, Collins has made considerable progress, a recovery captured by filmmakers James Hall and Edward Lovelace in their feature-length documentary The Possibilities are Endless. It’s an unsentimental and unmannered portrait of one of Scotland’s best-loved musicians, but how did the pair gain his trust?

‘I didn’t make this film in any way; they suggested it to me, and I just let them get on with doing it,’ says Collins, while his wife Grace Maxwell makes coffee for us in their Highlands home. ‘I think I was a bit nervous when they started filming me in the studio, but Ed and James reassured and relaxed me; they gave me space so that I could be content with what I was saying and how I was saying it.’

We’re talking post-referendum (Collins switched to Yes a few months before the ballot), and Maxwell notes that one complication of Collins’ condition was aphasia: ‘He doesn’t always answer the question you asked him,’ she says, and he dryly notes that a career in politics might await. It’s true that the conversation goes off in unexpected tangents, from shaving cuts to septic tanks, but gentle reminders from Grace keep things on track.

‘”The possibilities are endless” was a phrase I kept saying when I was in hospital, over and over again,’ says Collins. ‘Ed and James thought it would be a good title. But I never saw the film until they had a private screening for us; we didn’t interfere at all.’ Maxwell mentions that after five minutes of the screening, Collins leaned back and reassured the filmmakers it was ‘good so far’.

The Possibilities are Endless uses some archive footage, but generally focuses on the working musician Collins is now. ‘After my stroke, I found it hard to remember the words to songs like 'Ghost of a Chance'; it’s not simple to sing,’ admits Collins. ‘It took me ages and ages, trying to relearn it, and the first time I performed it, I was a bit ropey. But I’m proud of these lyrics, particularly the middle eight on that one.’

And with that, Collins launches into ‘Ghost of a Chance’, perhaps not as popular as ‘A Girl Like You’ or ‘Rip it Up’, but one of his best, taken from the album Hope and Despair and featured in this new film. Embracing a back-catalogue is a key part of any artist’s development; for Collins, returning to and developing his music has clearly helped him find his way back to his many friends and admirers. ‘I can’t tell you what a huge role social media has played; so many lovely people out there. I love to laugh now. You won’t get any angry words from me.’

The Possibilities are Endless is on iTunes from Mon 20 Oct, and on selected release from Fri 7 Nov.