Scot Squad stars Karen Bartke and Darren Connell on treading comedy's thin blue line

The duo are on our screens in BBC Scotland's police mockumentary reprising their roles as po-faced desk sergeant Karen Ann Miller and her eternal tormentor, incorrigible but loveable man-child Bobby Muir.

With the show in its third series, their double act as Officer Karen dealing with Bobby's catalogue of antics – think stunt kites, mobility scooters, dodgy CCTV, a stolen face and heroic banana-eating marathon – has become a favourite.

When we meet in the suitably themed setting of the former Sheriff Court building in Glasgow (now the swish Citation Taverne and Restaurant) the contrast to their comic alter egos couldn't be starker.

Bartke's laidback demeanour is the antithesis to the stiff, bun-wearing, buttoned-up persona of her namesake, while Connell's off-duty style is light years away from Bobby's ubiquitous Parka and retina-searing, psychedelic wolf-emblazoned sweatshirts.

What does carry over, though, is the effervescence of their on-screen chemistry. They have a shared sense of humour and the knack of finishing each other's sentences that is forged in strong friendship.

Some viewers, it seems, would be keen to see that develop into something more. Connell – blushing to the roots of his hair – recounts one such story which involved a taxi driver asking if the pair had been romantically intimate.

Bartke roars with laughter as he blurts out the tale, not repeatable verbatim in a family newspaper. "When people start talking about whether we are going to get together, that is a bit weird," she says.

"Officer Karen is fond of Bobby and it is quite a maternal relationship. If you asked her about it she would probably say: 'I tolerate him' but secretly, within the depths of her hard, flinty police officer soul, she would miss it if he wasn't there."

Protective big sister perhaps best sums up her relationship with Connell. Bartke clearly dotes on her co-star who, unlike Scot Squad's Bobby, is shy and takes a bit longer to come out of his shell.

The pair admit to being surprised by their popularity. "I do feel like I'm hanging on to Darren's coat tails," muses Bartke. "I'm the one being dragged along in his wake because he comes up with such funny stuff."

Connell swiftly interjects. "No way. We're like macaroni and cheese – you can't have one without the other. I'm macaroni and Karen is cheese. Or you can be macaroni if you want?"

Bartke gives a wry smile. "It's fine, I'll be cheese," she says. "I'm the Paul McCartney and you are the John Lennon, all edgy and stuff."

Spending time with Connell and Bartke is a bit like falling down the rabbit hole in Alice in Wonderland. Any notions I had about how our interview may pan out are soon balled up and tossed in a corner.

Be it Bartke showing off the impressive hyper-extension in her elbows (they're super bendy) to Connell revealing his ability to hum and whistle at the same time (uncanny and oddly mesmerising), they make for hilarious company.

The vat of caffeine may be partly to blame. Bartke, 44, is fresh off the sleeper from London having spent five months working with the BBC Radio Drama Company, while Connell, 29, has been burning the midnight oil for his show at the 2017 Glasgow International Comedy Festival.

Attempts to kick-start the bleary-eyed vibe have resulted in much drinking of coffee and several pots of strong tea as they recount their adventures in showbiz.

While Glasgow-born Bartke had dreamed of an acting career since her teens, it wasn't until 2010 that she took the leap of faith, leaving her job as a research and development manager for a company which sold property search reports to conveyancing solicitors.

"I joined Glasgow Schools Youth Theatre when I was 16. I considered applying to a drama college but lost my nerve," she says. "I went to university, got a job afterwards, joined an amateur theatre company and was a hobby actor for a long time.

"Obviously being an actor is difficult because you don't have a steady income, but I thought: 'To hell with it, I'll try it for six months.'"

Bartke hasn't looked back. She was spotted by Scot Squad creator Joe Hullait while performing at a comedy improvisation group and invited to audition for the Comedy Unit-produced show.

Around the same time Bartke landed a part in the acclaimed My Name Is, based on the story of 12-year-old Molly Campbell from Lewis who, in 2006, was alleged to have been snatched and taken to her father's native Pakistan. It later emerged the youngster had gone of her own accord.

After a successful UK tour, the Sudha Bhuchar-penned play was adapted by BBC Scotland for Radio 4. Bartke won the 2016 BBC Audio Drama Award: Best Debut Performance for her role in it.

Last spring, she was awarded the prestigious Norman Beaton Fellowship and joined the BBC Radio Drama Company on a five-month contract which saw her rubbing shoulders with the likes of Josie Lawrence, Sheila Reid, Miriam Margolyes and Neil Gaiman.

Bartke showcased remarkable versatility by performing in more than 30 productions including Gaiman's Stardust ("I was such a fan girl") and the opening two episodes of Harry Hill's remote prison drama Life On Egg.

"I was also a Russian seagull in Watership Down and a 6ft tall, Australian PE teacher in Wild Things," she says. "It has been an incredible job and I'm gutted it's over. I would love to do more radio. I like that you can do such infinite variety of things and are not restricted by what you look like. It is hard to sound 6ft tall on the radio, but I think I pulled it off."

Connell, who was nominated for Bafta Scotland New Talent Award in 2015, has grafted equally hard. "I'm not trained as an actor," he says. "Everything is self-taught."

Prior to landing his breakthrough role in Scot Squad, he spent almost a decade working as a supermarket trolley collector in his hometown of Glasgow. "I'm quite similar to Karen in that when I was younger I wanted to do drama but was too shy to pursue it," he says.

"When I was working as a trolley boy at Asda I always dreamed of doing comedy. I studied television production because I thought that might help get me in. I tried to be an extra but I never got any jobs.

"My first big thing was a crime reconstruction about the Ice Cream Wars. I played a character called Fat Boy. They put a mattress down outside the STV studios and I had all these guys jumping on top of me. I lay there thinking: 'At last, I'm an actor!'"

Away from Scot Squad, he is steadily building his reputation on the stand-up circuit. Connell had a run of sold-out shows at the 2016 Glasgow International Comedy Festival with Trolleywood, a semi-autobiographical offering about family life, heartbreak and weight struggles.

He made his solo debut at the Edinburgh Festival Fringe last August and will return to the Glasgow International Comedy Festival in March with his new show, Darren Connell: No Filter. In recent days, he has launched an eponymous podcast that is fast clocking up listeners.

Their respective stars may be in the ascendant, but Connell and Bartke are taking little for granted. Connell recalls how during the fledgling days of his career, he took various jobs to help pay the bills.

"Struggling actor and all that, my pal said I could come and help him clean windows," he says. "He asked if I was scared of heights and I said no. I also needed be under 15 stone – which I wasn't – because the ladder only supports a certain amount of weight."

He bites back a smile. Bartke's shoulders are already rocking with silent mirth. "I'm scared of heights, weigh at least 16 stone and up these ladders thinking: 'What am I doing?' I had been told at one house: 'Watch that rose bush. It belongs to an old woman and she is obsessed with it.'

"What happens? I manage to slip and fall with my arse landing right on top of the rose bush. I arrive back at the van with my shorts ripped and legs cut to bits. My pal's dad – the boss – straight away says: 'Did you fall in that rose bush?'

"We went back to look and there, right in the middle of the rose bush, was this big human-made print from my arse. He is usually such a serious guy, but he just buckled. The pair of us were doubled over, crying with laughter."

Reflecting on our conversation later, it strikes me that Connell's backside is something of a recurring theme. At one stage he talks about undergoing colonic irrigation in the name of research, inspiring a memorable Scot Squad scene involving Bobby, bits of carpet and an old Lego brick.

Then there was the time a 17-year-old Connell decided to get a tattoo. "I saw this amazing Native American portrait and wanted to get that on my chest right down to the belly button," he says. "But the guy in the shop said: 'That's €700' and I only had €70 …"

What does €70 get you? His childhood nickname "Darrenski" written in Comic Sans on one bum cheek, apparently.

"Years later I was at home with a horrible hangover and wearing this massive XXXL tracksuit from Primark. I went to get an ice lolly from the freezer but as I bent down my arse popped out and my mum spotted the tattoo. She was like: 'What the f*** is that?' I said: 'Er, I think it's dirt …'"

"Sometimes I forget I've got it. I remember being in the shower and my ex-girlfriend asked if I had a tattoo on my arse. I thought: 'Whit?' I'll say to people: 'Nah, I would never get a tattoo …'"

Since we're barrelling down the path of questionable life choices, it only feels right to ask if either of them has ever had a run-in with the law.

Connell recalls how, not long after turning 18, he heard his cousin was throwing a party. He rocked up and knocked on the front door. When nobody answered, he wandered into the back garden. A neighbour – seeing a suspicious figure creeping around – called the police.

"I was really naive and a bit tipsy," he cringes. "I kept saying: 'I'm just trying to get into the party,' when the house was clearly empty with all the lights off."

To make matters worse, Connell's elder brother Martin – whom he had left a note telling about the party – turned up. Soon both were being questioned by the police. It turned out the party was being held in a friend's house nearby.

"My brother was raging," says Connell. "There was real tension building and it started to get quite heated. Afterwards he was like: 'You almost got us the jail.' The police officers quickly realised 'this guy is just daft' and that it wasn't anything malicious."

Bartke tells a story about the time delinquents set fire to the conifer in her garden. "The entire thing was up in flames like a Roman candle. The fire brigade arrived and the kids across the road in the park are shouting: 'There's a fire! There's a fire!' Then someone came past and said: 'We saw the wee arseholes that did it, they have been setting light to stuff all the way up the street.'"

The police turned up next. "There was an experienced police officer and a probationer who took my statement. She was writing it down in torturous detail: 'I saw the wee arseholes that did it …' "Three-quarters of an hour in, she said: 'Oh, I've not written down what you do for a living.'

"I replied: 'I'm an actor.'"

Bartke mimics the policewoman doing a comical double take.

"She says: 'Wait, are you Officer Karen?'"

In her spare time, Bartke sings in a classic rock 'n' roll covers band called The Sentinels. "We do the police hockey gig every year," she says. "This year people wanted to get selfies for the first time. Last year, though, was when I became conscious that the police were really getting into the show.

"They seem to love it. I'll tell you what, Scottish police officers have got observation skills second to none – they can spot you from a mile away. Other than a girl in Boots one time, nobody else knows who I am or recognises me.

"Last Halloween I dressed up as a 16th-century washer woman ghost in a mob cap with my face painted black and white like a skeleton. I was sitting on the Fish Cross in Ayr when, from the other side of the street, this random guy – who it turned out was a policeman – shouts to me: 'Excuse me, are you Officer Karen?'

"When I said yes, he replied: 'We talk about you in the office all the time. We're convinced you guys have got someone on the inside. C'mon, tell me, whose notebook do you have?'"

She and Connell would love to see Scot Squad return for a fourth series. "I'm so chuffed to be a part of it," says Bartke. "I watch it as a fan as much as anything. While a lot of humour lately has been quite biting and negative, I feel ultimately, at its core, our show has a wee bit of heart in it."

Whatever the future holds, Bartke is sanguine. "I've been going with 'every day is an adventure' since I left my day job," she says. It is a sentiment echoed by Connell. "I'm just enjoying the ride. Until I need to go back to pushing trolleys."

Scot Squad is on BBC One, Wednesdays, 10.40pm. Thanks to Citation Taverne and Restaurant (citation-glasgow.com)