Ahead of the DVD release of Bill Forsyth's movie debut, film critic Mark Kermode explains why he has been in tune with the filmmaker since their first meeting.

Three criminal masterminds sit in their car, making small talk about the weather and discussing spectacular suicides. They don't realise it yet, but they're about to plan the heist of the century…

No, hang on. This is a Bill Forsyth film, so that can't be right. Start again.

Three naïve Glaswegian teenagers sit in a car and talk about their boring day. One admits that he's just tried to kill himself by choking on cornflakes. The film cuts to outside as they're joined by a pal. The car, we now see, is a tireless wreck that's been abandoned on wasteland just off Maryhill Road. The scene even has time to fit in a random running joke involving the visual gag of a boy jogging in a red tracksuit.

That's more like it. That's a Bill Forsyth film: one with an undercurrent of social reality that's not approached head-on but at an angle via whimsical comedy and a certain cloudy outlook on life. Not only that: this is That Sinking Feeling, the film that set the template, made by Forsyth on a budget of next to nothing, using a cast drawn from Glasgow Youth Theatre, but now getting the high-quality dual format DVD and Blu-ray release it deserves as part of the British Film Institute's Flipside series.

Forsyth had been making documentaries and sponsored information films for the better part of a decade before he shot a frame of That Sinking Feeling. In truth, he'd already written the script that would become Gregory's Girl but couldn't get funding for it and, desperate to try his hand at a fictional feature, used the limited resources that were at his disposal.

It was a make-or-break time for Forsyth: he tells the tale that, around then, the sameone edition of the Evening Times featured him in a local-filmmaker-makes-good story on the news pages and listed him among the sheriff's warrant sales on the back pages. The result, in any case, is one of the funniest Scottish films ever made, with at least one genuinely brilliant gag slipped into every scene. The story is daft: Ronnie (Robert Buchanan) gathers together his mates in order to steal stainless steel sinks that cost £60 a piece from a plumber's warehouse and so make their fortune. That's pretty much it, even though the heist plot device doesn't actually intrude into the action until after the half way mark.

But That Sinking Feeling isn't really about narrative or genre or market-researched audience expectations. The heart of the movie lies in its essentially fond but occasionally dark juxtaposition of the lovable characters and an environment that's filled with tenement rubble, Tongs graffiti and kids that could have been plucked from an Oscar Marzaroli photoshoot. It beats to the Glasgow patter rhythms of its non-professional cast, often improvising, creating a succession of comedy sketches that work within the framework of Forsyth's 40-page script.

The new DVD/Blu-ray release restores the original audio track to the film, complete with its sound effects, music cues and the original actors' broader tones (it was dubbed into "clearer" Scottish accents for an American cinema release in 1984, what Forsyth jokingly calls "the Edinburgh version", which was also used for the 2009 DVD release). Even so, the characters remain as far from the hard man myth of 1970s Scotland as they could possibly be, more in need of the tweezers of drag caper Some Like It Hot than the razors of gang drama Just A Boy's Game.

Sharing the commentary track with the director on the DVD/Blu-ray is film critic (and self-confessed Bill Forsyth fanboy) Mark Kermode. There's a really nice rapport between the two of them, as the often shy and reticent Forsyth opens up to Kermode's questions and comments.

"The first time I met Bill was when I was sent to interview him by Time Out for Breaking In [Forsyth's 1989 crime caper starring Burt Reynolds], and I had to go up to Glasgow," Kermode tells me. "We ended up in a pub and started talking about the soundtrack of Local Hero. I said, 'You know that bit where there's that weird Mark Knopfler thing and it goes "Uh-euhhh-uh-ehh" and it's not even a note?' And he went, 'No, no, it doesn't go like that, it goes "Brup-brahhh-brah-brah".

"We sat in that room for, oh I don't know how long it was, attempting to sing that funny little opening bit from Local Hero. And I hold to this day that we bonded over our joint attempt to sing an absolutely unsingable piece of music from near the beginning of the movie. I've still got the little Dictaphone tape…"

Kermode has worked with Forsyth several times since - on a career-retrospective BBC Radio feature; on a Culture Show special in which they went to the re-opening of the village hall in Pennan to watch a screening of Local Hero; at Screenplay, Shetland's annual film festival, where Kermode and his partner Linda Ruth Williams are curators and where, in 2012, they programmed the restored version of That Sinking Feeling. It was during this last collaboration that he grabbed a camera crew to capture something for his Kermode Uncut blog which is now included among the DVD/Blu-ray bonus features.

"Bill had with him a plastic shopping bag and I asked 'What have you got in there?'" Kermode remembers. "And he said, 'I've got the receipts, all the paperwork, for That Sinking Feeling.' He literally had this bag of receipts which included the most unbelievable things: 50p for the electricity for making the lift work for half a day in one of the scenes, that sort of thing. One of the items they had to account for was just 'meat'.

"The astonishing thing was, when you added them up together, it turned out that That Sinking Feeling was genuinely, at the time, the lowest-budget properly-released feature film ever made - and it made it into the Guinness Book of Records. Maybe it's still in there. It was an extraordinary indication that what he'd done was made this film from the ground up with almost no resources at all, other than what he had in front of him, which was this group of players and his own extraordinary sensibility, which is very comic but also melancholic and insightful."

Kermode agrees that the essence of Forsyth's style rests on his experience as a documentary filmmaker coupled with a dry sense of humour, although he also believes that Forsyth has a very poetic sensibility. "I think he is genuinely a poet at heart … A poet who just happens to write with a camera."

The poetry in That Sinking Feeling might have been written using cheaper materials than most, but it's definitely still there on the screen, more than three decades later. And the film looks surprisingly good on a technical level too, a testament to the professional crew who donated their time on the three-week shoot free of charge.

Oh, and by the way, I listened again to Mark Knopfler's soundtrack for Local Hero. The bit they were talking about actually goes "Burrrayah-dap-dah"…

That Sinking Feeling (12) is released on the BFI Flipside label on April 21, priced £19.99, www.bfi.org.uk