THE admonition "never work with children or animals" is widely known in acting circles - and from the gates of St Trinians to the ramparts of Hogwarts, it has been just as widely ignored by generations of British actors.

"Never work with family" is one you don't hear quite so much. But it's advice which has been treated with equal disregard by everyone from filmmakers Joel and Ethan Coen to artists Jake and Dinos Chapman. For them and others like them, the potential artistic synergies outweigh the risk of the occasional familial spat.

Veteran actor and director David Hayman agrees. His much-anticipated revival of John Byrne's play The Slab Boys opens at the Citizens Theatre this week, and if you run your eye over the cast list you'll see not only his name (twice, actually: as well as directing, he plays Mr Currie), but also those of David Hayman Jr and Sammy Hayman.

The first, at 28 the eldest of Hayman's three sons, is assistant director on the production, while 26-year-old Sammy plays lead Slab Boy Phil McCann. That's also the role Hayman Sr filled at points in a theatrical odyssey which began in the late 1970s and ended with him staging Byrne's entire Slab Boys trilogy at the Citizens Theatre as part of the 1983 Mayfest.

But wait, there's more. Later this month the Glasgow Film Festival screens the world premiere of Wasted Time, co-directed by David Hayman Jr, scripted by playwright Martin McCardie and also featuring dad. Shot in HMP Barlinnie in a fortnight on a budget of just £12,000, it's the first feature from Shooters Films, an offshoot of Spirit Aid, the global humanitarian charity Hayman Sr set up in 2001.

So, in a spacious dressing room backstage at the Citz, I meet both Davids to talk about the perils and pitfalls of working together, about Slab Boys and Wasted Time, about masters and apprentices - and to try to unpick the finer points of what is fast becoming a creatively profitable family business: Hayman & Sons.

"You can't beat nepotism," says Hayman Sr, laughing. "But no, I've always worked with my boys. I'm very close to my three sons because we work together in Spirit Aid, we work together in Shooters, so we've always had a really collaborative experience. We're talking still about further work that we're going to do together and I love exploring that idea."

This "exploration" has already seen Hayman Sr feature in several of the Shooters shorts, and last year the working relationship moved onto a new footing when he drafted in David, then working as a director on BBC Scotland's River City, to help with his one-man show The Pitiless Storm. It tells the story of a trade unionist and dyed-in-the-wool Labour man who, on the eve of the referendum, renounces the OBE he is due to collect and decides to vote Yes. Hayman, who was very firmly in that same pro-independence camp, still wears his blue "Yes" band proudly on his wrist.

"There were a lot of emotional changes within the play and the emotional graph was quite complex, so after a couple of days of rehearsing I decided I needed a director and I asked David to come in," he explains. "He made all the difference, which was lovely, so I really enjoyed working with him. It's always good to have someone out there that you trust. I think David's instinct is very good, and certainly he's proving very good with Slab Boys." He was also, Hayman adds, "kind of tough".

And how did David Jr find the experience? "It was a big change for me," he says. "Going from something like River City, where you're basically in charge of a 40-man crew, and then coming onto something like The Pitiless Storm where it's a one-man show was really interesting."

So interesting that after his work on Slab Boys and an upcoming stint on River City he's returning to the stage in October to direct a Tron Theatre revival of McCardie's play Damaged Goods.

A question, then, for Hayman Sr: could you have worked so closely and amicably with your own father?

"My dad's tough," he replies. "I love him to bits but he's a tough, cantankerous old bastard. I did start working with him, because he was an electrician in an engineering yard in Glasgow and that's where I started out as an apprentice. In his heyday he was a man's man, a typical hard-working, hard-drinking, west of Scotland product. A strict disciplinarian." He pauses to chew on the question a little more. "He would have been tough to work with," he decides after a pause.

Among young men of his background in the late 1960s, Hayman was far from unique in deciding ultimately not to follow his father into a life as "a wage slave" in Glasgow's heavy industry. But it didn't make the resulting family ructions any less easy to manage.

"I suppose it's a societal thing, that the sons follow the father, and I suppose my generation was the first to break away from that," he says. "I remember my father being very angry when I said I wanted to be an actor. Automatically your sexuality comes into question and all the rest of it. And I guess that was a threat to my father. I wasn't accepting the role model he was presenting for me, I was rejecting it. So he had a quite violent reaction to it. He was very, very unhappy."

Perhaps in light of that experience, Hayman's own thoughts about his sons' future careers stayed private and his mouth stayed shut as they were growing up. Instead of trying to diminish their horizons, as Glaswegian fathers of previous generations might have done, he promoted a doctrine of latitude allied to a strong sense of personal morality.

"I always said to my boys, 'I have no investment in what you do with your lives, it's who you are as human beings that I have an investment in. You can be a bus driver or a brain surgeon, I don't actually care, as long as you're a decent human being.'"

Carrying through on that, David Jr initially had no plans to follow his father into the world of theatre and film, despite being taken onto sets as a boy and having his eyes and ears filled with the sights and sounds of the movie business. He has early memories of seeing an original Slab Boys poster in a frame somewhere - between father and son they decide it must have been in Hayman's sister's house - but admits he hadn't read the play until shortly before he began working on this production.

"I left school at 16 and I didn't really know what to do," he says. "My favourite subject at school was PE so I did a sports coaching course in Glasgow but dropped out after half a year. But then I got involved in a media programme called the Govan Initiative when I was 18. It was only three months but we got to make a music video and I got to direct, act, handle the boom and the camera and editing equipment. And I suppose I just fell in love with it."

"But at the same time," laughs his father, "I'd come home and if I was on telly in something, the boys would go 'Zap! Let's see what's on the other side'."

But while David Jr set out on a different path to his father, at least initially, Sammy and 20-year-old youngest son Sean clearly didn't get the memo. Sammy has recently graduated from the Glasgow's Royal Conservatoire of Scotland, and Sean is currently living in Madrid as part of a film and media degree at Stirling University. Give it five years, and this Hayman trio could become a quartet.

But there was one exception to the laissez-faire nature of Hayman's fatherly advice: he told his sons he never wanted to see them take a job that required a uniform. No surprise, perhaps, from the man whose breakthrough screen role was as Jimmy Boyle in John Mackenzie's 1979 film A Sense Of Freedom and whose debut as a film director came with Silent Scream, a biopic of another notorious inmate of the Barlinnie Special Unit, Larry Winters. A convicted murderer, Winters died in prison of a drug overdose in 1977, aged just 34.

There are many constants in David Hayman's life and career - his political engagement, the Citizens Theatre, Glasgow, even The Slab Boys itself - but prime among them is the Bar-L. From his first visit there in 1972 to run arts therapy courses in the company of Giles Havergal, then three years into a long stint as artistic director of the Citz, to his most recent outing in Wasted Time, Hayman has been a regular visitor.

"I continued to go along to the Special Unit [after 1972] because I thought it was this incredible powerhouse of creativity in the middle of this Victorian prison," he says. "Jimmy [Boyle] was writing and sculpting, Larry [Winters] was playing music, writing poems, doing paintings. People found a creative expression for themselves which transformed the qualities of their lives. So I really believed in the work they were doing."

As well as visitor, he also became observer, critic, penal reform campaigner and, courtesy of a memorable hour spent in Larry Winters's cell one night, apt pupil.

"I was rehearsing Hamlet here at the Citz and I would go along to Barlinnie twice or three times a week in the evening," he says, taking up the story. "I remember Larry Winters sitting me down in his cell and saying 'You want to know about Hamlet? You sit on my bed.' And he gave me this hour-long treatise on the psychology of Hamlet which was extraordinary and illuminating. I wasn't getting that in the rehearsal room, I was getting it from a lifer in Barlinnie who had an empathy with Hamlet and knew where he was coming from."

If there's any sense of a baton being handed on from Hayman to his eldest son, it's this preoccupation with Barlinnie. Hayman Jr has already made several films there and it's a safe bet that Wasted Time won't be the last, given that the rationale behind Shooters Films is to make issue-based films.

Its other guiding principle is to use non-actors where possible, so as well as professionals Neil Leiper and Brian McCardie, brother of Martin. Wasted Time features performances from Barlinnie inmates. Their contribution reflects the film's genesis in improvisational workshops and interviews that Martin McCardie, Hayman Jr and co-director Moe Abutoq conducted ahead of shooting.

"We sat around in a circle and Martin went around and asked them about their experiences," says Hayman Jr. "He asked them to name one happy moment from their childhood and none of them could. Then he asked for a bad or a sad memory and everyone said something. So we took stories from each of them and Martin went away and wrote the script. So it's real in a lot of ways."

And how much of the film's £12,000 budget went on Hayman Sr's fee? "I got a bacon roll," quips the man himself.

Payment for his current Slab Boys shift may be equally nominal but then that isn't the point. Bigger things are at stake: celebrating the 70th anniversary of the Citizens Theatre, for instance, by means of one of the great works of contemporary Scottish drama.

"It is a real classic," says Hayman. "It's a wonderful play. It's a celebration of working-class life, I think, and a celebration of language, our west of Scotland vernacular that John uses so creatively and imaginatively. And it's a celebration of aspiration. I think the best line in it is where, out of that slab room of broken dreams, Phil McCann kind of cartwheels out the door at the end and says: 'Hey! Giotto was a slab boy!' It just shows that all young people have dreams."

But Hayman's revival of The Slab Boys has a personal aspect to it as well. He tells me why, beginning his story in the moments after the curtain fell on that epic 1983 Mayfest production, when he and Byrne faced each other in the Citizens dressing room.

"I said, 'John, I've given you four years. I've directed all three plays. I've played Phil McCann. I've taken off the wig and I now take off my dust coat and leave it to the next generation.' But over the last 30 years I've always toyed with the idea of going back and introducing it to a new generation."

That this new generation includes two of the three Hayman boys makes this revival even more perfect. So, three decades on, aged 66 (he turns 67 tomorrow) how does it feel to be back in the company of Phil, George and Hector, old friends being given a new lease of life? "Feels great," he says. And as his son looks on, he grins like a kid.

The Slab Boys is at the Citizens Theatre, Glasgow from February 12 until March 7 then transfers to the King's Theatre, Edinburgh (March 10-14). Wasted Time screens at the Glasgow Film Theatre at 2pm on February 28 as part of the Glasgow Film Festival.