"You can ask Duff about sex, substance abuse, Axl Rose and his near-death experience after his pancreas burst. But he can't talk about his fund-management company right now."
If that sounds an unusual instruction before an audience with one of rock's foremost hell-raisers, then Duff McKagan, bassist with Guns N' Roses when the band carved a new chapter in debauchery, is no ordinary rock star.
The Seattle-born musician, 48, experienced the "insanity" of life inside a 100 million-selling juggernaut when Guns N' Roses' 1987 debut album, "Appetite For Destruction", became a global phenomenon.
Trapped on a tour bus with Rose, a volatile, tantrum-prone singer, McKagan responded by indulging in cocaine and drinking half-a-gallon of vodka a day, before switching to red wine (10 bottles daily) when he reluctantly embarked upon a health-kick.
Yet the Duff who strides into the Pall Mall hotel lobby looks the picture of health, as befits a musician who has a new career as a best-selling author and financial adviser to his less numerically-literate, guitar-toting peers.
He delivers his sage advice through his Meridian Rock wealth-management company for musicians.
McKagan discovered his acumen for business when the years of bad living caught up with him in 1994. He was hospitalised with a ruptured pancreas, which left him with third-degree burns, and a doctor's warning that he would die if he had another drink.
"There were a few days in hospital that were just flashing images," says the musician, who has been sober for 18 years. "My mom had Parkinson's and I saw her come in crying, seeing her youngest son on tubes. That turned me around."
McKagan found a new obsession – income tax returns. "I didn't have any work to do and I had files of my personal and Guns N'Roses financial statements for the previous eight years. I wanted to learn how to read these but I didn't trust anybody," he says. "I just got a lightbulb in my head and said 'I want to go to school'. That began my journey, taking accountancy and business classes at Seattle."
Today McKagan uses his experience, relayed in a Duffonomics column for Playboy, to advise bands: "When the record company pays you an advance, it is just that – an advance. And it's at worse rates than any bank would charge you to pay them back. Plus they'll charge you for all kinds of crap you don't ever see."
McKagan balances his business studies with the life of a jobbing musician, touring with his bands Loaded and Walking Papers. An autobiography, It's So Easy (And Other Lies), topped the New York Times best-sellers list, opening up a new literary avenue.
On Tuesday night, he embarks upon his hardest gig yet – presenting the Classic Rock magazine Roll of Honour awards at the Camden Roundhouse to an audience of his peers including ZZ Top and Lynyrd Skynyrd.
"There's no script so I'll just have to improvise," he says. "I'm honoured because those guys in the room are heroes to me so I just want to do those people as much justice as I can."
There could be an awkward moment since the nominees for Band of The Year include the latest version of Guns N'Roses, which Rose is hawking around the world's arenas.
McKagan quit the band in 1997, but despite remaining on good terms with guitarist Slash and other founder members, a full reunion remains a concert promoter's dream. The mercurial Rose is, as ever, the sticking point.
McKagan replicated the band's stadium-straddling success with his supergroup, Velvet Revolver. Now he is more than happy pursuing a downsized music business philosophy which last week brought him to the Yardbirds club on a wet, Wednesday night in Grimsby.
"In rock 'n'roll, we don't sell records at all like we used to," he admits. "Yet the artist still has to pay to make records. So you've just got to get out on tour and be smarter about your merchandising. Bands now charge $50 for a T-shirt, a CD and a meet and greet with fans."
If McKagan has a regret it's that he did not have his business acumen in 1988 when Fox rang to say that they planned to name a beer after him, in honour of his prodigious alcohol intake, in a new animated series.
" I knew nothing about branding yourself then or the royalties off it. I just thought cool, they wanna use my name and boom, The Simpsons was born. Yeah, if I had a nickel for every time… but it's fine."
The 1988-model Duff, hammering out the bassline to Welcome To The Jungle would barely recognise the mountain-biking, sober, happily married father who uses long-haul flights to tap out 4,000 words on a lap-top instead of a line of white powder.
"I don't think I would change anything," he says, even if it means slogging to the Humber Estuary for a gig. "They say 'will you really be there on a wet, rainy night in Grimsby?' Well we were there on that wet, rainy night."
Q&A: Quick queries
Where was the last place you went for dinner?
We didn't have a proper dinner in Grimsby. The chicken salad sandwich from Pret A Manger – that's one of the best foods I ever had.
What was the last album you bought/listened to?
Chateau Brian, Brian James from The Damned's new record
What was the last book you read?
A Battle Of Britain book on my Kindle
What was the last gig/concert you attended?
Last night, the Walking Papers
What was the last sporting event you attended?
Seattle Mariners baseball game
What was the last film you saw?
The Perks Of Being A Wallflower – I went with the whole family, it had some great life lessons for guys my age.