MONDAY, March 16 will be an unusual day for Fred MacAulay.

Bar holidays, it will be the first weekday in nearly 18 years that he hasn't done his BBC Scotland radio show.

He jokes that for listeners it will be like the ending of Jim Carrey film The Truman Show, when the lead character steps out the door and the studio stops transmitting.

"People will switch on and say,' Fred's not there. Oh well, I wonder who else is on then?" he laughs.

Behind the banter there's a touch of sadness in his voice as he looks back on nearly two decades at the helm of the popular morning radio show.

"The last show is Comic Relief day so there will be no excuse for any maudlin feelings," he smiles. "I'm not thinking about it.

"The good thing about doing a radio show, a live chat show, is that once you get in and you're concentrating, what is happening outside the four walls and in the real world doesn't count.

"Yes, the thought of leaving after 18 years could play heavily."

He won't be disappearing from the airwaves, the stand-up comic turned presenter will be hosting a panel show called Breaking the News and is involved in other projects.

Meanwhile he's going back on the road with a new comedy show, Twenty Fifteen, kicking off at the King's Theatre for Glasgow International Comedy Festival on March 28.

"I'm looking forward to doing much more stand up," he says." I've always been able to keep my hand in. When you look at 2012, for example, I did a full run at the Fringe, then a tour of England and Wales in the autumn.

"To get ready for that I was doing club gigs, so one way or another I did about 100 stand-up gigs in 2012. Other years I've maybe struggled to do half a dozen. But I've always been able to do something or other."

What keeps him coming back to perform is the sheer buzz of working in front of a live audience. There's nothing like it, he says.

"There is no secret that when you're in the Stand Comedy Club and it is going well it is an unbelievable feeling.

"I've not had the same experience of arenas that a lot of the other comics have had. I would imagine that the buzz is just even greater."

With that reference to the rising tide of superstar comics who play to sell out arena audiences, I wonder if he feels them snapping at his heels.

"It's a different world," he shrugs. "The analogy I use is like professional football - there are the young Wayne Rooneys earning £300,000 a week and old journeymen footballers and that was their entire career earnings.

"You just have to look at Kevin Bridges' achievements. If you ask, what is the difference between him and me? I'd say, about 30 years.

"With the change in the radio thing, I'm looking at what kind of audiences I pull in. I'm questioning what my relevance is to the audience and whether the topics I talk about are still relevant.

"I was thinking, I did a huge chunk last year about pensions and retirement. What 25 to 35-year-old is going to come to hear that?"

When the figures are examined - Fred is a former accountant, after all - it seems his audience is mainly made up of employed people maybe just a little older than himself. No wonder his material regularly hits the mark.

"The people who come to this show will see a completely different show from last year at the King's," he says.

"By the time I get to Edinburgh it will be a completely new show from last August. It's a lot of work but it's the nature of what we do, keep having to come up with new material. It's something I beat myself up about a lot. I do like to try and keep it fresh. I am by no means the most prolific.

"I was down working in Newcastle doing a weekend of stand up just a month ago, trying out new ideas, thinking what I've got in the repertoire that would work and there was a guy on who I had seen maybe three years ago and his 20 minutes was exactly the same. He's doing fine, he's got a nice living and all the rest of it but you should always be pushing yourself on a wee bit."

A stalwart of the Edinburgh Fringe, Fred has performed there for the past 27 years, as well as doing a radio show from the capital for the past 13 years.

It is a punishing schedule but he clearly seems to have thrived on the challenges.

When he looks back over his career the highlights are many, performing in places as far afield as Hong Kong, Australia and America and on his radio show getting the chance to meet Monty Python members as well as the likes of fellow comics Eddie Izzard and Paul Merton.

"I ski in the States and what I now do is I fly out to Los Angeles, pick up wee gigs and then go and do my skiing and maybe get another gig on the way home," he explains.

"I even gigged when I was skiing in Aspen. There was a gig in Snowmass in the Silver Tree Hotel. I phoned and said I'm a Scottish stand-up comedian. They said, send us a tape but we get hundreds a week. So I sent in a tape and they phoned me back and offered me the gig.

"I just love that kind of challenge because over here the audience know me and that's why they've come along. Standing up in front of an audience of 300 people in the Rockies, and they haven't a clue who you are, is a real challenge. You get the same buzz you got 25 years ago."

Despite the warm affection for his radio show, the Perthshire man who has lived in Glasgow for more than 30 years says he will never be the city's favourite son.

"Maybe it's some of the material I do," he muses. "One line I have is that I've been here for 31 years but I'll never consider myself to be a Glaswegian because I still have the ability to mind my own business."

It's just as well Fred likes to engage with hecklers in the audience, a few might have something to say when they see him at the King's.

Fred MacAulay: Twenty Fifteen, King's Theatre, Glasgow, March 28. Visit www.glasgowcomedyfestival.com