KNOWN as the porridge-oats hunk to breathless fans, Rory McCann's image as a solid oak of manhood was shaken to the roots in a public toilet. As his towering 6ft 6in figure leaned over a urinal, he was accosted.

''At the crucial moment this bloke grabbed me by the arm and said 'You're that porridge guy'. He looked me up and down and said 'My, you are big'. There is no way to get a flow going after that.''

McCann, advertising sensation and now star of Channel 4 cult comedy The Book Group, tells his toilet tale while rocking precariously on a high stool in a Glasgow coffee shop. He's huge for the flimsy seat and curses as he hunches forward to keep his balance on its spindly legs.

The idea that he is famous seems to surprise him. ''Why do people want to interview me anyway?'' Yet he is no longer best known for being the muscle man in the Scot's Porage Oats ads who lets cheeky girls peek up his kilt. The 33-year-old former lumberjack, tree surgeon (he still loves climbing into leafy branches where he can disappear), and one-time painter of the Forth Bridge, is today a respected actor following the cult hit of his current project, The Book Group. A Channel 4 success story, the intelligent comedy drama, now in its second series, is set in Glasgow and revolves around a set of dysfunctional people drawn together through their love of writing and a desire for friendship.

It's quirky and the humour is

bitter-sweet. Inevitably it's been compared to a Scots version of the US comedy, Friends. McCann plays Kenny in a wheelchair, a part he researched by meeting people in the spinal injuries unit at the Southern General hospital in Glasgow, and socialising with wheelchair users. ''Those guys were fantastic. They put up with me asking them the most ridiculous questions,'' he smiles broadly.

''How do you climb up the stair in a close when you're in a wheelchair? I had to find out and then do it. I even asked one guy how he made love to his girlfriend who also uses a chair. The people I spoke to were brutally honest and would always say if I did something or used my arms in a way a wheelchair user would never do. They were mainly very positive about the role. It was a good challenge for me as an actor too, taking me away from the obvious 'big guy' parts people would expect to see.''

He's got a cold, and had growled the fact in quite a disturbing manner when I first introduced myself, but now there is a major thawing as he succumbs to a hasty bribe of coffee and several hundred bagels with cream cheese.

A joke about his healthy appetite is greeted with indignance. ''Did you see that newspaper story about me needing a body-double in the latest porridge ad?'' he asks between chews. He is referring to a fitness guru being used as a stand-in for the McCann six-pack in his third, porridge adventure which shows him emerging from a skinny dip in a chilly loch - kilt swinging from a nearby branch.

''That really pissed me off, I mean, the guy quoted said I had a wee willie, which is bad enough, and not true (his voice is full of comic menace) ''But making out I was fat? I was in the process of losing weight after a film project.''

McCann's eyes flicker as passers-by stop outside our window and point nervously through the glass at him, as though they were observing a dangerous zoo animal, but his conversation doesn't falter for a second. He seems to be used to the attention. ''The adverts made me a familiar face, but I'd refused to do them at first.''

I ask him if he's subsequently become a hit with women, only to find out (apologies to his fans) that he has been for six years living quite happily with his girlfriend. She's a doctor, a very sensible girl, who takes it all in her stride, he assures me.

Even the steamy scenes in The Book Group?

He grins: ''I do have loads of girlfriends in this series. Kenny is a popular bloke. It's rubbish what actors say about being embarrassed by the crew staring at you when you're half naked and rolling around with a woman - it's actually great.''

He grins wickedly before admitting that he was actually deeply afraid during the whole Book Group creation - especially the first series. At the time he was an unknown quantity, had never done more

than a couple of ''one-line wonders'', as he describes his former experience.

''There were times at the start of it all when I would be standing, terrified in front of the cameras and people I considered 'real' actors. I had no idea what was happening, what the guy with the clipboard did, or if people in the studio were looking at me because it was their job to look at me or because they thought I was making a mess of things. Luckily everyone was very supportive and Annie Griffin steered me through it. I was in tears more than once though.''

Griffin, an American director and writer is the creative talent behind The Book Group. There have been questions asked on how she managed to capture the Scots psyche when arguably a more home-grown offering such as the BBC soap River City missed the mark. ''I think Annie's ideas work because she came into Scotland from the outside and has been able to observe us for who we are,'' says McCann.

''I've known her for a long time. She took a real chance on me by giving me the Book Group role. The first time she told me her idea for Kenny, who is based on me, I'm ashamed to say I told her he wasn't a good idea. She was a bit crushed, by all accounts, and I was obviously wrong.''

While ''Kenny'' lost the use of his legs in a climbing accident, the actor who plays him almost died a few years ago when climbing in Yorkshire with no ropes - falling 80ft. ''I remember clinging to rocks with my fingertips and there was nowhere for me to go, only down,'' he says. ''I knew I was going to fall, and that I'd probably die. I ended up just letting go. It was lucky that I rolled most of the way down and just broke my feet and wrist and bashed my head.''

Life was precarious but fun in his pre-acting days. He recalls: ''I was a lumberjack for years, a pub bouncer, I've sung in a band, in fact I still sing, and I even trained myself to be a tree surgeon. Now that was dangerous, hanging off of dead trees and sawing away at the branches. I also had a job swinging 250ft from a rope, painting the Forth rail bridge, I tell you though, acting is far more scary.''

After getting into showbusiness late in life, at last, he has gained the confidence he needs to be an actor. ''I'm a different person from the wreck of the first Book Group series. I've grown into it all.''

He has just finished filming a new project with Ewan McGregor and Tilda Swinton, and he has a forthcoming part in a television drama starring Kelly McDonald. ''My roles aren't huge but it's a start,'' he says. ''I've also got a chance of filming in Malta for a few months with my own slave girl and chariot. It's a lot better than cutting down trees but I'd go back to that before taking parts I'm not happy with. I want to make good choices after Book Group. I'm hopeful that I've made a breakthrough now and people are getting to know me.''

Illustrating the point, a well-dressed coffee drinker with a clipboard, looking every bit a television executive, appears by our seats and slaps McCann hard on the back. ''We think you're wonderful. Good job,'' he barks, before sweeping away.

The porridge-oat man smiles broadly, then turns to me and frowns. ''Who the f*** was that?''

The Book Group, Channel 4, Fridays, 9.30pm.