AN overcast June morning and on an industrial estate in Clydebank a commotion is unfolding. A police car sits behind a grubby-looking white van to which the rear door has been flung open, releasing a swirling mist of dry ice.

A gaggle of women dressed in feather boas, cowboy hats and deely boppers are being helped from inside. They teeter unsteadily in high heels, sipping alcopops through straws.

Welcome to Scot Squad. The hit BBC Scotland comedy has newly returned to our screens for a fourth series starring Grado – real name Graeme Stevely – and Manjot Sumal as traffic cops PC Hugh McKirdy and PC Surjit Singh.

I hear Grado before I see him. Which is remarkable given he's wearing a retina-searing, high-vis jacket. His unmistakable, booming voice carries down the street. Beside him, the more diminutive figure of Manjot can be seen trying to diplomatically soothe the affray.

For those unfamiliar with the concept, the show is a clever spoof that mimics the fly-on-the-wall style of documentaries such as Road Wars and Police Interceptors.

The scene is titled "Disco Van" and revolves around a hen party gone awry. Hence the colourful props.

Manjot and Grado (everyone uses his nickname) are one of several pairings in a Scot Squad cast that also includes Jack Docherty, Jordan Young, Sally Reid, Karen Bartke and Darren Connell.

Their on screen alter egos are chalk and cheese.

PC Singh is strictly by-the-book (he didn't hesitate to give his own mother a speeding ticket in one memorable episode), while PC McKirdy is a larger-than-life maverick (who has no qualms about changing his underpants in the front seat of the squad car).

Once the cameras stop rolling, how much does that odd couple persona mirror the real-life relationship of Grado and Manjot as colleagues?

Manjot: "Pretty much the same."

Grado: "We are completely different folk in terms of what we like. He likes going to the pictures and I hate going to the pictures."

Manjot: "Grado is very outgoing and I'm more reserved."

Grado: "So, what you see on screen is quite true to life."

Manjot: "But he is more intelligent in real life."

Grado: "Just a wee bit."

The second location of the day is a car park opposite Farmfoods at Baljaffray Shopping Centre on the outskirts of Bearsden.

As the crew begin setting up, Grado and Manjot happily chat about their lives.

Manjot, 36, grew up in the St George's Cross area. His late father Malkit worked in the Koh-i-Noor restaurant, while his mother Sukhvinder still works as a cleaner at Glasgow University.

The younger of two children, Manjot recounts a tough upbringing. "It was quite rough, especially being an Asian kid in that area due to racism. There was a group of kids who if they saw an Asian guy, that was it. One of my neighbours was beaten up quite badly and put in hospital by them."

He aspired to be an animator, but later gravitated towards writing and directing. In his early twenties Manjot saved up money from a job in a pizza shop to travel to Vancouver where he spent three months working behind the scenes on the TV series Smallville.

That sparked a love of acting and back in Scotland he joined a community theatre group. Manjot was directed by Cora Bissett in a handful of plays and did a stint as a radio presenter for Awaz FM before landing his breakthrough role in Scot Squad.

Married to Mandy, 33, he is based in Renfrew. Among his most recent roles was a part in Mariem Omari's verbatim theatre play, One Mississippi, which highlights mental health issues among men.

Grado, meanwhile, fell in love with performing as a wrestling-mad teenager. The 29-year-old, who is the youngest of three children, hails from Stevenston, Ayrshire. "The tap end," he clarifies.

His father John is a taxi driver and his mother Maureen, now retired, used to work in a hospital kitchen. He still lives in his hometown with his girlfriend Kerry Burns, 27. The couple have been together for 11 years.

Grado first caught the eye of casting directors thanks to Burnistoun co-creator Robert Florence who had watched his homemade wrestling videos on YouTube and shared them with the Comedy Unit.

That led to an audition for Scot Squad, with Grado also cast in the pilot for The Sunny, co-written by Florence and fellow comedian Iain Connell. Around the same time he was the focus of a BBC Scotland wrestling-themed documentary called Insane Fight Club.

He went on to a role in River City and joined the roster of US-based Impact Wrestling which saw his star rise on the other side of the Atlantic where it is ranked second largest only to WWE.

Grado will appear in the latest series of BBC Scotland sitcom Two Doors Down next year.

Away from work what are their passions? "Macaroni cheese," replies Grado without hesitation.

He's also a bit of an aviation geek. "I love planes," he enthuses. "I have a passion for flight. I love watching cockpit videos of take-offs and landings, aborted take-offs and landings, bird strikes …"

He pays £1 a month to subscribe to the Glasgow Airport webcam. One of his favourite things is to use the FlightRadar24 website to track flights or watch planes take off on the webcam and then run outside to watch them fly over his house in Stevenston.

"I love eating food, going out for my dinner and wrestling," he adds. "This is geeky but every night before I go to my bed I try to watch one wrestling match. How many have I watched over the years? Millions. I like watching old stuff from the 1980s. I love obscure stuff from Japan."

As for Manjot? He rattles off his own list. "Photography, going out for drives, drawing, watching movies and writing screen or theatre plays."

What is it like to be back in their police uniforms?

"To be honest, I feel more comfortable in my wrestling Lycra," says Grado. "This is quite uncomfortable to wear for 12 hours a day. I don't know how polis can do it."

"Aye, it's heavy," adds Manjot.

"The steel toe cap boots, layers of clothing and then having to run about daft?" continues Grado. "Nah, I prefer the comforts of my own leotard."

Scot Squad is on BBC One, Wednesdays, 10.40pm