The West Midland-born star of the hit detective series McDonald & Dodds, now in its second series, was a small child when he was introduced to a performer who would have a profound impact on his career.
"My mum took me to Bridgnorth to a clown class, I suppose I must have been six, I suppose," says the actor, who was born in Albrighton.
"I remember going up these sandstone steps, I can still see those steps now, to a theatre, where the class was being taken by a mime artist called Ben Bennison.
"I think he had appeared in Vision On, and I went into his dressing room with my mum, where he painted a red nose on my face, he was really great. It all came back to me when I went to Rada when I was 20, as Ben Bennison was my tutor."
You could say fame has been a long time coming for Jason. After decades of playing secondary characters on both stage and screen, the 58-year-old has seen his profile grow enormously in the past few years, and he is now once more taking centre stage in the new series of McDonald & Dodds.
The unashamedly twee whodunnit series, which sees Jason play the role of the bumbling but brilliant Det Sgt Dodds, has been a surprise winner in the battle for ratings. During the first series, more than six million people tuned in each week to watch Dodds' unlikely partnership with the slick whizzkid Det Ch Insp Louise McDonald. And while some of the sniffier critics point out that the gentle detective drama does not exactly break new ground, its popularity, like Sgt Dodds, shows the perils of underestimating the underdog.
Jason says he is not in the least bit surprised by the success of McDonald & Dodds, with its combination of complex murder mysteries, quirky characters and the stunning backdrop of Bath's Georgian architecture.
"It's such fun to make, I like playing interesting characters," he says. "I hope we will make a few more."
The present series was made last summer, during the brief hiatus from the lockdown, but social distancing restrictions were still in place.
"We were all in different bubbles," he says. "Me and Tala (co-star Gouveia) were in one bubble, and Rob Brydon was in our bubble too.
"We had a screen up if we had to walk past the camera crew, and while on set we have what is known as a 'rolling lunch', where you pick up your food when you have a moment rather than going back to base and eating together."
Jason says there was a brief scare during the first week of filming, when two of the team tested positive for the coronavirus.
"That shook people up a bit," he says. "They turned out to be false positives, but it reminded everybody why we have got to observe social distancing."
Despite these challenges, Jason is acutely aware that, as a TV actor, he is lucky to have been able to carry on working during the pandemic, while many of his peers who rely on theatre work have not been so fortunate.
"My wife, Clara Francis, was appearing in the West End, in Leopoldstadt by Tom Stoppard, which had been received so well, but that was suspended," he says.
"The Government has helped in some respects, giving money to the great institutions such as the National Theatre, and rightly so, but I think it needs to follow it through with some support for actors. It's been a very difficult time for actors and crew members."
Jason was born in 1962 at Windsor Road, Albrighton, on a smart new estate which had recently been built close to the village's railway station. He was only eight years old when his family moved away, but recalls some of the happiest years of his life.
"Alan, my dad, was a metallurgist, and he got a job at a company called Marston in Wolverhampton," he says. "The family was from the north-west, and my older brother was born in Oldham. I think for a while my family lived in a flat in Brewood Hall for a while."
"They moved into 12 Windsor Road in Albrighton, it might have been a brand new house, and that's where I was born.
"I loved it. At the back of the house was Donington Woods, and I had many happy memories of playing over there, and making dens in the various nooks and crannies around the station.
"My mother Mavis was a teacher at the primary school, I think it was in Newhouse Lane, and I went to the same school, but I was in a different class. I had some friends Guy and Philip, and I remember going to St Mary's Church with the school.
"I remember one year I had a loaf of bread to take to the harvest festival, and when it was my turn to walk down the aisle, I tripped, and the bread was scattered all down the aisle.
"The circus used to come down and perform in the village. There was a small estate with a green there, and the circus used to come and perform there."
With hindsight, it was perhaps inevitable that Jason would end up as a character actor, given his fondness for putting on different personalities as a child.
"I was never an extrovert, I was never precocious, but I liked to be a mimic. I loved putting on different voices and pulling faces," he says.
His first recurring TV role was as estate agent Gerry Fairweather who appeared in 11 episodes of EastEnders during 1987-88. He played Gene Hunt's solicitor Colin Merrick in Life On Mars,
But while Jason's love of playing 'character' roles has won much admiration in the industry over the years, he says it can also make for a slow-burning career, as the parts he played do not get the attention of the lead roles.
It was probably his portrayal of Chris Jefferies, the retired schoolteacher who was public pilloried after being wrongly suspected for the murder of Joanna Yates. which truly catapulted him into the public eye. His years of experience playing background characters came to the fore in the 2014 TV film The Lost Honour of Christopher Jefferies, with his uncanny capture of both the appearance and eccentric persona of Jefferies winning him many plaudits.
"I've never been a leading actor, and if I did get a leading actor's role, it would be because there was some strong characterisation in it," he says.
"For most character actors, it takes time to get established, because people will look at what you have done before when casting roles. That's probably why I am enjoying my greatest success now, in the middle of my career."
Other notable roles have included former prime minister Harold Wilson in royal drama The Crown, and former Montgomeryshire MP Emlyn Hooson in A Very English Scandal, a big-budget drama about the downfall of former Liberal leader Jeremy Thorpe. He also played Simon Harfield in the BBC satire W1A, and Tim Ifield in Line of Duty, as well as appearing in two films in the Nativity series.
He has recently returned from South Africa, where he has been filming Around the World in 80 Days for Netflix, which stars David Tennant as Phileas Fogg.
"It was great fun, and I was fortunate that we got back before we would have had to stay in an hotel, although I did have to go into isolation," he says.
And what next?
"I'm not one for big ambitions for the future," he says. "I would like to do a bit more film work. And hopefully, a few more McDonald & Dodds."