THE hearty laugh of Alex Norton crackles down the line. I've asked him who is the worst for "corpsing" – actor parlance for breaking into unscripted mirth – while filming the BBC Scotland comedy Two Doors Down and he doesn't hesitate to point the finger.

"Elaine C Smith," he says, referring to his co-star who plays overbearing neighbour Christine in the suburbia-set sitcom. Although it is hardly her fault: the one-liners she is tasked with delivering have a knack for tickling the funny bone.

"She has all the ridiculous lines and often finds something funny in the middle of saying it," says Norton. "Elaine has this extraordinary ability to be in two mental places at the one time. There is the character and there is her standing outside the character, listening to what this character is saying.

"Sometimes Christine will say something and then Elaine will burst out laughing. You can see her trying to stop when the camera is off her, but the shoulders start to shake, there's a little tremor. That gets the rest of us. We're gone."

It is five years since Two Doors Down made its debut as a Hogmanay special. The show has grown to become must-watch viewing thanks to its whip-smart observation and wry humour as it astutely captures the quagmire of neighbourly relations in a Glasgow suburb.

Norton, 68, is sanguine when asked whether the cast envisaged that the award-winning comedy – which returns for a fourth series on Monday – would achieve such success and longevity.

"It's amazing, isn't it?" he enthuses. "When we did the first one, we didn't even know that it would become a series. It was just a one-off as far as we all knew. To have one series was a bonus and now to have four is beyond our wildest dreams."

Norton reprises his role as long-suffering Eric Baird alongside the brilliant Arabella Weir as his wife Beth. Doon Mackichan and Jonathan Watson play incorrigible duo Cathy and Colin, with Smith as the irrepressible Christine.

Graeme "Grado" Stevely and Joy McAvoy are now settling in as Latimer Crescent residents Alan and Michelle (much to the chagrin of a green-eyed Cathy) with Jamie Quinn as the Bairds' son Ian and Kieran Hodgson playing his boyfriend Gordon.

A wedding anniversary, a wake, a hospital stay and a housewarming are among the major life events in the latest series. There are some new faces too: Mount Pleasant's Alex Kirk and Maggie O'Neill, known for Shameless and EastEnders, guest star as Gordon's parents visiting from Yorkshire.

Co-written by Simon Carlyle and Gregor Sharp, there are echoes of sitcom greats – from Abigail's Party to The Royle Family – in the Two Doors Down formula, with much of the action centred on Eric and Beth's living room.

"One of the great heads of light entertainment said, 'Give me four characters on a sofa and I'll give you a sitcom …'" says Norton. "Although we sometimes say, 'Wouldn't it be great if they all went on holiday?' I don't think you need all that."

Norton and Weir have the straight roles – the calm in the eye of storm – as Smith, Mackichan and Watson whip up mayhem around them.

"I don't know if I could play one of the other characters," muses Norton. "I love doing this role. What makes me laugh most when I watch good comedy is people's reactions to things.

"Arabella and I react a lot to what is being said. That can be just as funny when you see the impact of what has been said land on somebody and their slightly glazed or stunned reaction."

He may delight as Eric Baird but for many viewers Glasgow-born Norton will always be DCI Matt Burke in Taggart. He played the gruff telly detective from 2002 until the long-running STV crime drama was axed eight years later.

Norton clocked up almost 60 episodes as Burke. Yet, long before his alter ego ascended the police ranks to head the murder squad, there was a memorable turn on the wrong side of the law during a 1986 instalment of Taggart playing creepy butcher George Bryce.

The grisly storyline seems to stick in everyone's minds. "I wasn't actually the murderer but for some reason people seem to think I was," recalls Norton. "I was involved in getting rid of the bodies. And I came to a grisly end.

"We filmed the episode in the backroom of a butcher's shop where they did actually make black puddings. There was a machine and we were pouring in buckets of pig's blood." No corn syrup-based props here, then? "We did it for real," he confirms.

"One of the other characters in the butcher's shop was talking about these terrible murders and bits of bodies being found, then you cut back to me saying nothing and pouring a large bucket of blood. The implication was I was mincing these women up and putting them into black puddings.

"A lot of people stopped me in the street afterwards. They would say, 'Look, there's the butcher out of Taggart. See you? I've never eaten a black pudding since watching that …'"

A raft of successful Scottish actors – Alan Cumming, Douglas Henshall, Alec Newman, Stuart Bowman and Richard Rankin, to name but a few – had their screen debut or very early TV roles on Taggart. Was the show considered a lucky charm?

"I don't know about a lucky charm, but it is a rite of passage," says Norton. "There is a very elite club of people who have played dead bodies on Taggart. They probably meet up once a year."

There has been talk about a Taggart reboot led by Andrew Macdonald, who produced Shallow Grave, Trainspotting, Sunshine on Leith, 28 Days Later and The Last King of Scotland. I'm curious whether Norton has been approached to join that.

"I don't think I would be involved," he asserts. "My character would be far too old to be in the police force – he would be well retired by now. I doubt I would be back in it. Although if they asked me, I would certainly give it serious consideration.

"If they do it then it would be good to have a fresh team in there. The first rumour I heard – and it is only whispers – is that they would have Taggart's daughter heading the team because in the original series he did have a daughter who was very young.

"She would be the right age now, if she had gone into the police force, to head the murder squad. Personally I think it would be a great idea to have a woman lead the team and to also have someone called Taggart which would make sense with the title."

Norton lives in London with his wife Sally. The couple have three grown-up sons: Jamie, 21, has a degree in sound design and plans to go into video game design; Rory, 27, is teaching English in Japan; and Jock, 29, is in a band called Puppy who are due to release their debut album this month.

The actor admits that, while he doesn't get back to his native Glasgow as often as he would like, he still considers it home. "I always think of it as being like an umbilical cord," he says. "It doesn't matter where I am in the world, I am always drawn back to Glasgow."

Norton grew up in the Gorbals and then Pollokshaws on the south side of the city where his family moved when he was seven. "What is now Pollok Country Park was five minutes from my door," he says. "That was almost like my back garden where me and my pals would play.

"Although our house was just a wee room and kitchen, it was anything but a slum background. There was open air, freedom and joy."

Norton's upbringing was not without its share of adversity. He was only 15 when his mother Sarah died from kidney failure. She was just 39. Norton believes her death was linked to her consumption of once-popular headache remedy Askit Powders.

The over-the-counter painkiller, which is no longer available, was produced in Glasgow and mainly marketed to women. Askit Powders contained aspirin, caffeine and – until 1966 – phenacetin, which was later linked with kidney damage.

Norton is trying to secure backing for a documentary on the subject. As a child, he remembers his mother taking the powders – known for its catchy advertising tagline "Askit fights the miseries" – often several times a day.

He describes it as an "epidemic" that affected mainly working-class women. "By 1920, they were producing 20 million packets a year just for distribution in the west of Scotland," he says. "It is one of these things that has been quietly forgotten. Nobody was brought to book."

Norton first became aware of the link between Askit and kidney failure after watching a documentary some years after the death of his mother. It has always stayed with him and in the decades that followed he has often thought about pursuing the idea of a documentary.

"Most people in a similar situation who had lost a parent – usually their mother – like me didn't put two and two together either and realise it was connected to Askit. It was seen as being 'mother's little helper'. Families were torn apart by it."

His motivation, says Norton, is to tell the stories of those who were affected. "There can't be a legal recourse – the Askit Powders company doesn't exist anymore," he says.

The fire was reignited as Norton toured after publishing his autobiography, There's Been a Life, in 2014. "This lady came up to me at a book signing and said she was very friendly with an heir to the Askit fortune, because I had mentioned it in the book," he says.

"I thought, 'Christ, there are people living high on the hog off the profits of this pernicious bloody thing.' Do they realise the cost that funded their lifestyle and left them with a legacy? Do they realise what my legacy was? Or the legacy of hundreds of other families in Scotland?"

There is little doubt about the deep impact it had on his formative teenage years. After Norton's mother died, it left only him, his father John and younger brother Dougie in the family home.

"It was hard enough for me," he says. "But my brother was only five and had the tragedy of growing up without a loving mother. My mum's sister and my granny did most of the rearing of him. I left home at 18. I just had to go. I went to London.

"It was terribly hard for my dad as well. But there was that Glasgow thing where it was never discussed. Afterwards no one talked about it. You were just expected to get on with your life. That, for me, was a problem – although I didn't figure that at the time," he continues.

"I have since looked into it and learned if you don't have that grieving process, particularly when you are young, it can come out later as depression. And that is exactly what happened to me.

"When I was in my early twenties, I got terrible depression. I had no idea what caused it. You just think, 'Why am I feeling like this?' It never occurred to me that it was to do with the fact that I hadn't properly grieved my mother's passing."

An amateur pop psychologist might suggest this was why he pursued a life as an actor. Did the escapism appeal? Norton acknowledges that it was certainly a factor. "I knew I didn't want to be part of the life that was being pencilled in for me," he says.

His father aspired for his son to become a plumber. "A great trade and there are times I have thought that I wished I had listened to my dad and had become a plumber," says Norton.

"But I did want to get out of my background. I wanted to be more. And part of a bigger world. It is the old cliche about the working class that there is only three ways out: sport, showbusiness or crime. I wasn't very sporty and didn't fancy a life of crime, so showbiz was the only option."

Norton has worked steadily for more than half a century in theatre, film and television (his first TV role was playing a schoolboy in Dr Finlay's Casebook). Another early job saw him play guitar with the late David Bowie in the 1969 movie The Virgin Soldiers.

"It was before he was famous," he says. "We were in this film together as basically glorified extras. We were like the guys in Dad's Army, the ones who stand at the back of the squad.

"There were three weeks of night shoots. We were in Bury St Edmunds, it was November and freezing. It was meant to be the bloody Malaysian jungle in the height of sweltering summer and so we were wearing thin shorts and cotton Army shirts.

"Davy and I found out we both played guitar and would bring our guitars onto the set. It was meant to be a train wreck after an ambush and in the breaks between set-ups we would spend our time huddled in a railway carriage trying to keep warm. We would sing and play guitar.

"I didn't realise then that he was going to be one of the biggest stars in the world," adds Norton. "But I thought he was extraordinary. It was like: 'Wow'. When he started singing, it was fantastic. I remember thinking, 'Why is this guy bothering to be a glorified extra?'

"I didn't say it to him, of course. I can't say that I said, 'David, you should be in the music business …' and that he replied, 'Yes, you are right, Alex. I will do that …'" Norton breaks off laughing. "That never happened. But I realised he was something special."

As well as traditional acting roles, Norton has carved a niche in the video game market. "When my kids were growing up, they played a lot of video games. I used to watch them and realised that it was a real emerging market. I thought, 'This is the future'.

"With a video game you [as the player] are the star of it and go through the adventure. I am doing quite a lot of video game voices. I have become a wee bit of a star in the video game world."

Norton says his son Rory, while teaching English in Japan, earned major kudos points with a class of teenagers after he revealed that his father had voiced the character Rab in the hugely popular Dragon Quest franchise. "He called me afterwards and said, 'They went completely apes***.'

"I love doing video games. You get to play characters that you wouldn't play if you were cast in a film. I'm playing these ridiculous and outrageous characters – it is wonderful."

Two Doors Down begins on Monday, BBC Two, 10pm