A MUGGY August afternoon and the BBC Scotland studio in Dumbarton is a hubbub of activity. Usually it is River City being filmed here but today another gang is in town: Still Game.

As I walk through the gates, the exterior of The Clansman pub is being erected in the car park. Members of the art department bustle back and forth as couriers deliver packages containing props. A van arrives with a Harley-Davidson inside.

Within the hangar-like space of the soundstage are a smattering of sets, each bearing handwritten labels such as "Jack's kitchen", "The Clansman", "Isa's bathroom" and "Navid's backstore".

In the far corner is Victor's flat. The scenes have already been shot here and the set is being struck, two crew members carefully packing everything away.

Furniture is neatly stacked ready for removal and in the hall lies a heap of coats, shoes, umbrellas and a hat ready to be added to the already towering pile of boxes.

While the nameplates remain on Isa and Jack's front doors, Victor's is gone. There is an air of finality to it all. The end is nigh for Still Game.

The ninth series, which begins next Sunday, will be the last to grace our television screens. After 17 years (even longer if you count its earliest incarnation in a 1996 episode of comedy sketch show Pulp Video) the young-at-heart pensioners of Craiglang are bowing out.

As I watch filming, the action centres on Navid's corner shop. A monitor shows Isa – played by Jane McCarry – loitering by the door. Behind her head is a newspaper rack with stickers for the only three titles you need to read: The Herald, Evening Times and Craiglang Courier.

A few minutes later McCarry bustles off set and pops over to say hello. She has her blouse open and her breasts on show. Well, technically they are Isa's breasts, the flesh-coloured padding with its pendulous frontage prompting a hilarious double take. Talk about hanging out.

It's a humid day and with the temperature nudging 21C, McCarry is visibly wilting. And little wonder. Her costume comprises six layers: padding, polo neck, blouse, pinny, cardigan and coat.

That's just the top half. There's also the heavy skirt and thick tights, not to forget a wig and Isa's trademark furry hat – which McCarry has affectionately nicknamed "Ted" – atop her head.

Hence the gaping blouse. "Feel the quality of that," she says, thrusting an arm of her pink cardigan towards me. "All man-made fibres," chips in Sanjeev Kohli, who plays shopkeeper Navid, as he saunters over to join us.

The duo reveal that the lentils used to bulk out their padding as Isa and Navid can get a bit whiffy in this heat. "We smell like Scotch broth," says McCarry.

Between takes we settle down for a quick chat. Kohli immediately segues into dad jokes ("I could give you a recipe for herby fish, but I haven't got the thyme"). He points towards my notebook. "Make sure you write down: 'Top notch herb-themed banter …'"

How long does it take them to get back into the headspace of their Still Game characters? "Oh, about 30 seconds?" smiles McCarry.

Kohli pats the rotund padding beneath his costume. "It's the belly. As soon as it goes on, it changes my whole physicality and suddenly I'm Navid again," he says. "To be honest, people shout stuff at you in the street all the time so you never really stop being the character."

A stone's throw from where we sit is the set for River City, the day job for Kohli, 47, who has played Amandeep "AJ" Jandhu on the BBC Scotland drama series since 2015. Is that an odd juxtaposition?

"The other day Mark Cox was walking to set dressed as Tam and he looked over and there was Sanj as AJ," says McCarry. "He said it felt so wrong." Kohli grins. "It was like a rip in the space-time continuum," he quips. "I got a photo of me in the full Navid outfit standing outside the Oyster Cafe."

Did they expect viewers would fall so much in love with the double act of Isa and Navid?

"The moment was the live show, wasn't it?" says Kohli, referring to the sold-out 21-night run that Still Game did at the SSE Hydro in Glasgow in 2014, followed by a 15-night run three years later. McCarry nods. "It was amazing. That was the best job of my life," she says.

The live shows included a sketch where Navid and Isa paid homage to a romantic scene from the film Titanic. "We are on the poop deck of the ship," says Kohli. "And you have got 12,000 people in the Hydro wanting these two pensioners to get off with each other."

McCarry, 48, laughs heartily at the memory. "They were shouting: 'Get her pumped!'" she says. "It is weird because Navid is married. Anyway, we were meant to lean in closer and closer as if we might kiss and then the curtain would come down.

"The key thing is we mustn't ever kiss and cross that line. But one night the curtain didn't come down. Sanj looked at me and said, 'What do we do?' because everyone in the audience was screaming, waiting for this kiss."

Kohli strokes his fake beard. "What did we do?" McCarry laughs. "I think you dipped me," she says.

As McCarry is called back onto set, Kohli talks about how it feels to say goodbye to Still Game. "I don't think I have processed it yet," he says. "I can only compare it to the first time we stopped [in 2007], although we didn't know until afterwards that we weren't coming back.

"But in a weird way it never went away and I've got a feeling it will be like that again this time. I struggle to get my head around the fact that we have done it for this long. I can still remember the first time I had this on and looking at myself in the mirror.

"If you had told me then that I would still be doing this now, I would never have believed it. I'm not feeling sadness yet, but it will kick in."

What will he miss most about playing Navid? "The atmosphere on set and getting to say those lines," says Kohli. "The way that the boys [the show's co-creators Ford Kiernan and Greg Hemphill] have written Navid is that he parachutes in and gets the killer line.

"They are very generous that way; they give us the brilliant lines. I know Navid inside out, how he is going to deliver it and react to things. He doesn't always have to do the heavy lifting that perhaps Jack, Victor, Isa and Winston have to, but he gets the funnies.

"I love the way he has evolved. I tend to get to do film parodies, such as One Flew Over the Cuckoo's Nest or Breaking Bad, with Navid as this philosopher-warrior guy. It is fun and I will miss all that."

When McCarry returns from shooting her scenes, we finish up the interview in Kohli's Winnebago. A few bits and pieces of Navid's clothing, the ubiquitous woollen jumpers, polyester breeks, colourful shirts and ties – each item more garish and retina-searing than the next – hang in the wardrobe.

McCarry reflects on bidding farewell to Isa. "I genuinely believe she is real," she says. "Even though the TV show is ending, I feel she will still carry on somewhere out there.

"There is never another job where I will be so comfortable. Look at that shoe. You will never get a shoe more comfortable than that."

Her face grows serious. "What I will miss is the team being together. That's it now. We have been doing this since we were young and have shared this big journey in our lives. We will all still be good friends, but it is not the same as coming in every day to work like this.

"Ford was laughing so hard in that last scene that his moustache pinged off. There aren't many jobs where you would be so happy and comfortable and genuinely laughing as hard as that. I can't imagine ever doing a job like this again. It has been magical."

Is it bittersweet then? "No, there is no sweet," she asserts. "I'm glad that it has ended when it should end and we have not outstayed our welcome. Nothing lasts forever – good or bad. Everything has to end. It will be a grieving process for me."

The term Isa has become shorthand for being a nosy gossip. We all know an Isa … McCarry nods. "Everybody does. People don't always recognise me but, when they do, the first thing they say is, 'Guess what they call me?' I'll kid on I don't know and eventually they'll say, 'Isa!' Bless them."

Has the pair ever been tempted to nick some sweeties from Navid's shop during filming? There's a firm head shake from Kohli. "Not me," he says. McCarry glances over at him, a smile playing on her lips. "What? Never you, Sanj? Not even the odd one?"

Kohli reminds her that during the first couple of series, there was a rat problem in Navid's shop. McCarry grimaces. "I did eat loads before we knew there was rats," she says, shuddering. "I said to him when I was eating the cola bottles, 'What's those wee bits?' Then we found out it was rat droppings. We didn't eat them again."

Thankfully, they insist, in more recent years any potential nibbling vermin have been successfully thwarted. The final day of filming often sees a scramble among the cast and crew as they stake their claim on Navid's stock. Think Dale's Supermarket Sweep. Or as Kohli puts it: "It's like Saigon."

"Everybody goes crazy, pushing Ford and Greg out the way," adds McCarry. "Last year Greg – bearing in mind it is his show – got one Pot Noodle because the rest of us had swooped in like seagulls and taken everything. He came running in shouting, 'There's nothing left!'"

Their easy banter is testament to a working relationship and friendship stretching back more than two decades. They first met when Kohli began writing Chewin' the Fat radio sketches in 1997. "I did quite a few of those," says McCarry.

"But this was our first acting job together," says Kohli. "I hadn't been acting that long when I started this." McCarry looks at him fondly. "You were scared when you started this," she says. Kohli gives a wistful smile. "I totally was," he confirms.

She helped show him the acting ropes? "He is the man he is today because of me," jokes McCarry. "We are good friends and will always be close. I have known Ford and Greg since 1995. Mark [Cox] was the year below me at drama school in 1990. Gavin [Mitchell] was in Pulp Video in 1995.

"We all go back such a long way. We have grown up together. That is why it is so hard. It is great meeting up and chatting but it is not the same as being with someone 14 hours a day."

Kohli uses the analogy of Geri Horner (nee Halliwell) talking about the Spice Girls phenomenon and how only the five of them in the band truly knew what that experience was like. "It is a bit like that with Still Game, which is pretty special," he says.

McCarry recounts standing backstage at the SSE Hydro as the Still Game gang prepared to perform live in front of 12,000 people for the first time.

"It was like being a rock star," she says. "The music was blaring." She looks down at Isa's cardigan. "Well, a rock star dressed like this … It was the weirdest feeling in the world. I remember saying to Mark, 'Oh, my God!' He replied, 'Dressed like this, we can do anything.'

"That is the power of this show. If I was to go out onto that stage in any other job or circumstances, I would have died but I felt strong because we all had each other. It was insane. I have never taken heroin but I would imagine it is …"

McCarry trails off, realising that analogy could be problematic. A pause. "Like fizzy cola bottles," she concludes. "Or mainlining raw Lemsip," adds Kohli.

They will return to the SSE Hydro with the rest of the cast this autumn for a final farewell stage show. Before then, series nine of the TV show will arrive on our screens next weekend.

As it gets closer to the end, will they see Still Game out in style? "Do you want to have a party at your house, Sanj?" asks McCarry. Kohli looks like he is considering it. "That is something we have never done," he muses. McCarry is warming to the idea. "We should have a wee party," she insists.

Is this really goodbye? "When you see it, it feels final," says McCarry. "It will be emotional and special when the last episode airs."

Still Game begins on the new BBC Scotland channel next Sunday (February 24) at 9pm. Further episodes will be shown on Thursday nights at 10pm

Thanks to Moxy Glasgow Merchant City (moxy-hotels.marriott.com)

In tomorrow's Scottish Life with The Herald on Sunday: we go behind the scenes with Still Game co-creators Ford Kiernan and Greg Hemphill