On the morning we meet, Glasgow seems especially delighted to have Craig Ferguson back in town. From the taxi driver who deposits him at the city centre cafe, to the waitress who reserves our table, to the punter who stops him for a selfie as he’s walking across George Square, there a buzzy warmth and a no-arguments sense of ownership to how Ferguson is received on the street.

The pally familiarity is not surprising: despite basing his career in the US for the past 25 years, Ferguson’s broad frame and hairily handsome features are pretty recognisable. He did after all spend nine years presenting CBS’s Late Late Show, which at its peak topped the ratings of both Jimmy Fallon and Conan O’Brien. He stepped down in 2014 and James Corden took over, while Ferguson went on to win two Emmys with his new gameshow for the same network. And then there’s a roll-call of standup specials and movie credits (he wrote and starred in the charming Saving Grace with Brenda Blethyn), not to mention one of American comedy’s highest accolades: addressing the White House correspondents’ dinner. “This is just another case of immigrants taking jobs Americans don’t want,” he told the dinner guests.

With Desmond Tutu on The Late Late Show with Craig Ferguson, 2009. Photograph: Francis Specker/Alamy Stock Photo

Now the 57-year-old is back in Scotland – his younger son goes to school in Glasgow and he caught his Vermont-born wife saying “umnae” (am not) the other week – and ready to perform his first standup show at the Edinburgh fringe for a quarter of a century. “I’m a little nervous because it’s the first one I’ve done here in a long time – and I don’t know if it will be different or not. I think nerves are healthy. I want it to be good.” What makes a good show? “If you get lost in it – not just saying jokes but thinking of ways to tell a story and improvise. It’s hard to put your finger on.”

Observers of the late-night TV scene in the US now consider Ferguson an innovator, with his surreal puppet sidekicks and bizarre flirting routines. He made the genre his own, mostly through his ability to tread a fine – and occasionally uncomfortable – line between belly laughter and genuine revelation. His 2009 interview with archbishop Desmond Tutu, for which Ferguson won a prestigious Peabody award, is a fine example: the South African cleric giggles helplessly as Ferguson probes him about the washing facilities during his visit to a Darfuri refugee camp. In anyone else’s hands, it would be catastrophically inappropriate, but Ferguson balances the interview acutely, resulting in a moving meditation on the nature of suffering and forgiveness.

Ferguson also remastered the comedy confessional for the late-night audience. His 2007 monologue about Britney Spears, who was at the time experiencing a very public breakdown, has been watched millions of times, and is frequently referred to as an online resource for people struggling with addiction. It’s another trademark balancing act: at first the studio audience laugh along as he tells them his “aim has been off” and promises them “no more Britney Spears jokes”. The key change is faultless as he continues: “Because this weekend she was checking in and out of rehab, she was shaving her head and getting tattoos – and this Sunday I was 15 years sober.”

Watch Ferguson’s monologue about Britney and alcoholism.

In Riding the Elephant, his memoir published earlier this year, Ferguson writes candidly about his alcoholism – how his toxic drinking nearly derailed his early career – and is honest enough to take the reader beyond the “happy ever after” moment to set out the challenges of living life in recovery. Ferguson moved to the US in 1993, a year after he stopped drinking, having been talent-spotted by an LA agent at the fringe. He had his first major hit playing, ironically, an archetypal English toff in the ABC sitcom The Drew Carey Show, but he had already enjoyed considerable success in the UK, filming a sketch series with the BBC. His memoir suggests, however, that the move gave him a clean slate. “Nobody in Hollywood cared if I’d been a drunk or from the wrong social background,” he writes.

Having grown up in the new town of Cumbernauld, near Glasgow, Ferguson happily admits to a residual resentment about cliched reactions to his accent, but insists: “I don’t have that visceral barricade anger I had when I was 24. What I feel about class is that it robs everybody. A class structure that promotes people into positions they are not capable of is a disservice to everybody.”

It was anger that propelled his fondly remembered character Bing Hitler, a furious folk singer who eulogised his hatred for worms and the world in general from the stage of the Glasgow Pavilion in the mid-1980s. Would Bing Hitler survive today? “I think it would be fine. It was the name of a Scottish folk singer – that was the joke. The difference was I was angry at everything, but it wasn’t particularly cutting edge. One of the main things you get asked about if you work in humour is, ‘In this politically correct climate, do you find it frustrating what you can and can’t say?’”

Watch Ferguson performing as Bing Hitler in 1987.

I worry that he’s about to embark on an anti-millennial moan, but Ferguson is too nuanced for that. “As you get older, there’s a temptation to think things were better when you were younger – and things weren’t better when I was younger. I like the way kids are now. I think they’re interesting. They’re saying: ‘Let’s not be shit to anyone because they’re different.’ They’re kind.”

He sees this most in Glasgow, which has changed “so much for the better” since he left nearly three decades ago. He sounds quite bamboozled by the difference – his doting taxi-driver was telling him how great it was to see gay couples holding hands. Even seated, Ferguson is a big presence, but he has mellowed – or to be accurate, sobered – since Bing and his early years in the US when he grumbled about Scots not celebrating the successes of their brethren overseas. “I thought I was hot shit,” he says, “for getting a big-timey American TV show with my own name on it.”

He seems far more aware of his inner workings than your average west of Scotland male, though it’s hard to divine how much of that is recovery and how much prolonged exposure to Californian culture. Even so, it is clear that this interviewer doesn’t relish being interviewed. What if he had stayed in the UK? Would you have been like Peter Capaldi? (The pair played in a punk band in the early 80s) “Peter’s a very good actor,” says Ferguson quickly. “I don’t know how it would have gone. I like to think I would have become a beloved TV detective, but the worlds of ‘if’ are legion.”

It’s a stretch to imagine Ferguson fronting up a Glasgow version of Foyle’s War. His brain seems far too busy, his instincts too curious, and in that sense The Late Late Show must have suited him. But it’s hard to overestimate the relentless grind of hosting an hour-long daily show. “You start looking for ways to entertain yourself,” he says. “Guests would come back again and again and again, so you both have to find something to talk about. That becomes a thing.”

He accepts that the Trump era has radically changed the late night landscape, ushering in a far more political form of comedy. “I don’t know how I would be now, because to be non-political would be seen as political. If I’m honest, what really happened with me and Late Night was that I was having a great time but I got bored and I was ready to go.”

Ferguson is reluctant to take a position on Trump, or Brexit, or indeed Scottish independence, but it doesn’t come across as coy when he explains that he doesn’t want to alienate people for one very straightforward reason: it might stop them asking him for help. “I can’t tell you the number of people who have come up to me [since the Spears monologue] and said, ‘I got that.’”

In 2019, it’s not uncommon to hear celebrities talk openly about their struggles with addiction, but Ferguson got sober in 1992, a lifetime ago in terms of public acceptance. As you would expect, he welcomes more openness about mental health problems, but with caveats: “Openness is not knowledge,” he states very deliberately. “My own experience with alcoholism is not necessarily [like] anyone else’s. But I have found the most therapeutic thing I can do is talk to other alcoholics who have been in a similar situation.”

In his book, he seems to suggest that the idea of what people consider problematic has broadened too much over the past few decades. “Have we pathologised the human condition?” he says, putting it far more elegantly. “There is a temptation to think, ‘I should feel better.’ Why? I don’t feel OK all the time and I’m OK with that. If I felt good all the time, that would be weird.”

Ultimately, he remains both hopeful and realistic about the impact his own sobriety can have on others: “I know one thing – I know how you can stay sober if you’re an alcoholic, and if you want to know I can help you. That’s the only thing I know. It’s taken me 25 years sober to get this. Everything else is entertainment. The house, the life, the car, the stuff, everything else is gravy and where I really should be is in the ground in 1992. I’m fucking lucky.”