OVER the years we have encountered many incarnations of Sanjeev Kohli. There is Navid, the corner shop owner and king of one-liners in Still Game. There is the Mercedes-owning, tasselled loafer-wearing Ramesh (another middle-aged shopkeeper) in radio sitcom Fags, Mags And Bags. There is super-chilled Surjit in TV comedy Meet The Magoons, and oddball muso Synthesizer Patel in Look Around You.

And now, time for another one. In a quiet corner of the BBC Scotland canteen in Dumbarton, Kohli is talking about his latest alter-ego: Amandeep "AJ" Jandhu in River City.

This Tuesday evening, the suave and disarmingly charming AJ – a "local lad made good" according to the blurb – will make his entrance to the fictional Shieldinch. It is a stark departure from Kohli's usual comedy roles, marking his first foray into the world of TV soaps (or "continuing drama acting" as the man himself is wont to call it).

So who is AJ? Kohli sums up his character as a man whose relationship with his wife (played by Dawn Steele) hangs by a thread following his mid-life-crisis affair. With the betrayal still raw, a lot rides on their fresh start, as AJ, a former banker, pursues a long-held dream of running his own artisan pie-making business.

Kohli, 44, exudes a similar mixture of excitement and nervous trepidation about his own life-changing career move. He is acutely aware that River City fans have a fierce sense of ownership for the long-running BBC Scotland series. "With there being the two-month lag between filming and the episodes going out, I hope from a personal point of view that I'm alright," he admits. "I won't know until then. I have that to look forward to and hopefully I won't get lynched."

He cheerily concedes to feeling like "a bit of an interloper" when first encountering the "Who's Who of the Scottish thespian diaspora" mingling in the green room. "Given the volume of work to get through you don't get a huge amount of takes," he says. "The insecure Sanj thinks: 'Are they saying, "scene complete" because they have to move on or because they are happy with what I've done?' I'm always going to think I'm the weak link. The more I have done, though, I have felt more confident."

Still, it's not like Kohli just rocked up on set one day and demanded a part. He was headhunted by River City bosses who wrote the role of AJ with him in mind. "If you had said to me a year ago that I would get a part in River City, I would have assumed it was just a wee guest appearance," he muses. "They basically said: 'We have written a part for you', which is incredibly flattering."

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Producers told Kohli they wanted him to project a "version" of himself. "In terms of age profile I'm not playing a 63-year-old shopkeeper," he says, referring to his famed role as Navid in Still Game. "They told me: 'We are writing him to be quite fun, witty and warm.' Of course, you never think of yourself as being any of those things, but that is what they asked me to recreate."

In person, Kohli embodies all of the above. He is gregarious company with a canny line in tongue-in-cheek observations. Between mouthfuls of cheese toastie, Kohli regales me with tales of family life, his "geeky" childhood and "cosseted, middle-class" upbringing. He also shares no-holds-barred opinions on religion, politics and whether men over a certain age should wear skinny jeans.

Outside of work, Kohli's life is family-orientated and revolves around his wife and "weans". He is married to Fiona, 44, who works in the BBC Scotland music department. Kohli describes her as his rock and soulmate ("as many people have pointed out, she is actually the funny one out of the two of us"). The couple have three children: Ruby, 14, Bel, 11, and Vinay, eight.

"My weans are very much my life," he says. "They are at a fun age. Even Vinay has developed a line in sarcasm – I don't know where he gets that from." Kohli gives a mock roll of the eyes. "They are cracking kids and a really good laugh."

Born in London, the youngest of three sons (brother Hardeep is a well-known journalist and broadcaster, while Randeep is a senior police officer with London's Metropolitan Police), Kohli moved to Scotland with his family aged three, when they settled in Bishopbriggs near Glasgow.

His father Parduman was a teacher and mother Kuldip a social worker, but after relocating north of the Border, they ran a corner shop and later invested in property. Today, his parents live close to him in Glasgow's west end and, he attests, offer "a very good rate" for babysitting.

Kohli, who attended the private St Aloysius’ College in Glasgow, says he was an "incredibly shy, studious and bookish" child. "I did six Highers, three A-levels and nine O-grades – yup, I was that guy," he says. "I had no pals. I got sent by my very hardworking mum and dad – who had that middle-class Indian education ethic – to a fee-paying Catholic school across town.

"It meant I didn't have any local pals. All I really had was my school work and I was good at it, so I threw myself into that. When I think now of my own kids, all of their friends are local and they are at parties and sleepovers every other week. I didn't do one sleepover all the way through school."

Kohli's elder brothers were hugely protective of him. "Growing up as an Asian in Glasgow, aye, you got called the occasional name, but I had a very cosseted, middle-class Bishopbriggs, spam valley existence," he says. "I remember being incredibly shy, getting everything done for me and being scared to walk into shops on my own when I was 16 or 17. Asian boys are generally cosseted but to be the youngest of three? Very much so.

"I can see echoes of that in my youngest. He won't tie his own laces. I think: 'C'mon wee man, don't be like me.' I know I turned out OK, but I want him to be more independent than I was. Kids can go one of two ways: they either genetically inherit your awkward traits or they can see what you're like and rebel against it."

Kohli credits his comedy career success to a perpetual feeling of being outside looking in. "There were two Asian families in our neighbourhood. I was born in London, [had an] English accent, got sent to a Catholic school across town," he says, checking off the list on his fingers. "I was the outsider and you find a lot of people in comedy are like that. To make sense of the world, they look for comedy."

His path into the entertainment business wasn't conventional. Kohli studied medicine at Glasgow University but switched to maths, gaining a first-class degree before embarking on a PhD. After packing that in, he drifted into comedy when a university friend asked if he would like to be involved in a radio show she was making for the BBC called Ghetto Blaster.

By the late 1990s, Kohli was writing for BBC Scotland sketch show Chewin' The Fat, which starred Ford Kiernan, Greg Hemphill and Karen Dunbar. Kiernan and Hemphill later cast him in their pop cult phenomenon, Still Game, which ran for six series from 2002 until 2007. His star turn as shopkeeper Navid helped set Kohli on the road to becoming a household name (in Scotland at least).

Playing laidback Surjit in Channel 4 comedy series Meet The Magoons – which big brother Hardeep co-wrote and directed – further boosted his profile. During the noughties, he became a regular talking head on programmes such as 50 Greatest Comedy Catchphrases, 100 Greatest Sex Symbols and Most Annoying Pop Songs … We Love To Hate.

Kohli has gone on to garner a portfolio including roles in Fresh Meat, Bob Servant Independent and the big screen adaptation of Irvine Welsh's Filth. Last year he hosted BBC Scotland's light-hearted political bluffing guide, Blethering Referendum, and was part of the hugely successful stage show reprisal of Still Game, which enjoyed a 21-date sell-out run at the SSE Hydro in Glasgow.

"My route into acting has been very much through writing comedy and performing that," he reflects. "For a while it was just shouting in wigs. Then I got Still Game and there was more subtlety there in that it was delivering killer line after killer line, which was given to me as a gift."

People regularly come up to him in the street and quote lines from Still Game. On one occasion, Kohli was pottering around Ikea when a man thrust a mobile phone in his direction and begged him to do an impression of Navid for his wife. "Imagine being a footballer where half the city adore you and the other half want you dead? I'm lucky enough to be in a show which is almost universally adored so I will never take that for granted. Still Game has opened lots of doors for me."

Kohli is keen to start opening a few doors of his own volition. One ambition is to see his BBC Radio Four sitcom Fags, Mags And Bags make the transition to television. "I love it – it's my baby," he says. "As much as I adore Still Game I never wrote it. I have been obsessed with corner shops ever since we had one. We need to see the wall of crisps. We need to see the spinning rack of 99p graduation cards. I would love for that to be on the telly."

Equally, he would like to spin out some longevity in his current River City role. "There is every option for it to be long-term but the thing is I could be s***e – and they might not ask me back."

Kohli isn't shy about expressing an opinion. He describes himself as a "Sikh atheist" and in stark contrast to older brother Hardeep, chose not to wear a turban at an early age. "I had two religions in childhood: Sikhism and Catholicism – and rejected them both spectacularly," he says.

Sikhism, he asserts, is by far "the grooviest" of religions. "As a way of life it is pretty good, but I just reject the idea of God," says Kohli. "With any religion, all the old stuff, the hierarchies, creep back in. You have Sikhs who still believe in a caste system and are unhappy if their daughter marries outwith caste. Aside from the God thing, with any organised religion there is an implicit arrogance that 'our way is the best', which I think is fundamentally wrong."

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At Catholic school, Kohli says he embraced "everything but the three Cs: communion, confirmation and confession". He recalls a burning childhood curiosity about the confessional box. "I wondered how much the priest could see: was it latticed or like a two-way mirror at a police station?" he says. "I also wondered what a communion wafer tasted like. They always looked solid like a hockey puck."

During communion, he remained seated in chapel as his classmates clambered over him. "I could imagine them thinking: 'Heathen, heathen, heathen, proddy, heathen, heathen.' I felt like a flesh hurdle – yet another reason to feel out of place. I used to go to extra mass during Lent just to fit in. I even gave up chocolate for Lent once, but that was a hard shift because we had the corner shop."

A few years ago, his daughter Ruby asked: "Is it true that God has a long white beard and lives in the clouds?" Kohli was taken aback. "I assumed someone had said this at school, a teacher perhaps. I said: 'Ruby, where did you hear that?' She replied: 'I saw it on The Simpsons.'

"I have told my kids that if they want to believe in God, they should believe in God – but they need to come to that on their own. I have had some interesting conversations with the wee man about it. I think he wants to believe in God – but he also wants to believe in the tooth fairy.

"We lost a guinea pig and he asked: 'Dad, do you believe in heaven?' I said: 'Vinay, it doesn't matter what I believe it – it is about what you believe."

Politics is another subject Kohli talks frankly on. While Hardeep was an ardent Yes in last year's Scottish independence referendum, he admits to "dithering" over his own decision.

"Every room Hardeep went into he was trying to persuade people – and he tried to persuade me too," he says. "In the end I voted Yes, but I had a few things I needed to sort out in my head first. You had to give people the time to do that. A lot of people voted Yes and didn't arrive at it immediately because they did have insecurities and fear change.

"It got quite divisive and binary. That did annoy me because there had to be space for debate and dithering because it was such a big decision to make."

His River City character AJ has had a midlife crisis – something that Kohli can relate to. His own came in the form of a pair of skinny jeans. "I thought I could probably get away with them because I have a typical Punjabi build – a potato with four toothpicks poked into it," he says.

"I went to Topman and bought a pair. I returned them two days later. The shop assistant said: 'Do you mind if I ask what was wrong with the trousers?' I replied: 'Me. It was me that was wrong with the trousers.' I looked like an amputee spider.

"I thought: 'Right, I can't shop on the high street any more.' I probably still can, but I always have to ask Fiona first: 'Is this mutton dressed as lamb?'

"I genuinely have too many clothes, which is such a first-world, metrosexual worry. A pal is doing a clothes swap soon so I'm trying to have a cull. I want to look stylish rather than fashionable these days. But then, why do I care so much about my clothes? I should be more like Jeremy Corbyn."

Sanjeev Kohli is in River City on BBC One Scotland from this Tuesday, 8pm