The scruffy, long-haired guy in jeans and an Aqualung t-shirt looked like one of Jethro Tull's roadcrew. Except what roadie has a loaded pistol strapped surreptitiously to his ankle?
"I'd had some death threats, so we had a couple of undercover cops from the Denver Vice Squad dressed as roadcrew during a show in Border, Colorado," singer Ian Anderson explains calmly. "It was the early 70s and the person who'd made the threats was known to the police. They'd been watching his house but he'd escaped through a window and fled in a car, so there was genuine concern. Mercifully they didn't have to pull out their service pistols from their socks."
He smiles wearily and adds, "Another day in the life of Jethro Tull..."
Ian, 75 - fondly remembered for wearing a cod-piece on stage and playing the flute while standing on one leg - is one of rock's more thoughtful and original stars, famously incorporating elements of English folk, prog and classical music into Tull's eclectic sound.
So why would such a band attract homicidal headcases? Did some maniac harbour a grudge against unusual time signatures and traditional harmonies?
"A lot of people had threats from weird fans whose obsession had turned into hatred back then," Ian tells me. "We were lucky. Others like John Lennon were not.
"I've spent my life looking over my shoulder and being careful in crowds of people.
"I did have a bodyguard, assigned by the record company, around this the time. He came armed with a sword stick - a sword hidden in a walking stick. He lasted two days. He was more of a hinderance than a help."
Another Tull concert, at Denver's Red Rocks Amphitheatre in 1972, erupted into a full-blown riot. "The police over-reacted when fans turned up without tickets and used tear gas on people inside the arena as well as outside," he says. "It was before we played and there were ugly scenes.
"We did manage to make it on stage and perform but unfortunately the police wanted to take it out on someone and the band were fair game. We had to escape by hiding in the backs of cars covered by a pile of blankets."
By coincidence, Ian had tried to enrol as a police cadet in Blackpool in his teens. "They were interested until I told them I had O levels," he says.
Jethro Tull, who took their name from a radical 17th-century agricultural pioneer, are about to release RökFlöte - the 23rd studio album of their 56-year career.
The band broke big in 1971 with the multiplatinum Aqualung. The follow-up, 1972's Thick As A Brick, playfully spoofed prog rock concept albums - although most reviewers missed the joke.
Always a free-thinker, Anderson's work ranges from the Renaissance-inspired folk-rock of Songs From The Wood to recording Jeffrey Goes To Leicester Square on a three-stringed Russian balalaika.
Tull have sold more than 60million albums, five platinum-sellers, winning a Grammy in 1989.
Although never a 'singles band', Living In The Past and The Witch's Promise both went Top 5.
Ian estimates that he has performed fan favourite Locomotive Breath - about catastrophic population growth - live more than 3,800 times.
In recent years, he has played fund-raising Christmas shows in churches and cathedrals to help restoration work - he gives them all the ticket money, covering musicians, sound and lights out of his own pocket.
"Wherever we play I budget for two hours."
He praises the acoustics at Bradford Cathedral but says St Pauls and Liverpool aren't workable, joking "the architect should have been shot".
Although he doesn't call himself a Christian, grammar-school-educated Anderson appreciates the role of religion and the Church in society. "I don't have blind faith, but I believe in possibilities; perhaps probabilities."
He characterises himself as "an observer", taking a keen interest in science, nature and politics.
At Christmas, he played Bath Abbey, Exeter Cathedral for the second time and Gloucester Cathedral but says, "The night before their ancient heating system broke down, and the temperature was 3 degrees and dropping. It warmed up with the audience in place."
Ian cites Beethoven and Muddy Waters as his biggest musical influences. "Bach appealed when I was in my twenties but I've grown rather fond of Handel more recently."
He has toured with an orchestra but, Ian tells me, "I don't think I'll do it again - the logistics, the hassle, the cost, theatres with disappointing standards...".
He's gearing up for a summer of shows around RökFlöte, but only three are in Britain; two of them festivals.
"The title began as 'Rock Flute' but along the way, I toyed with the idea of changing to the old Icelandic Rök and Flöte which is German for flute, both with umlauts.
"The umlaut was appropriated by Motörhead and Mötley Crüe, and now ultra-right-wing fringe bands writing about Norse Gods, but that shouldn't be an impediment. It's like saying because there are a lot of love songs I can't do a love song.
"The challenge is to deal with the subject in more of a light-hearted way."
He sends himself up too, claiming that in his pomp he looked like "some demented Nureyev with a flute".
Jethro Tull retired in 2012, but Anderson revived the band five years later. Last year's critically acclaimed comeback album The Zealot Gene saw them back in the Top Ten.
Dunfermline-born Ian, who moved to Blackpool aged eleven, now resides with his second wife Shona, a cousin of the Duchess of Rutland, in an 18th Century estate set in 500 rolling acres of Wiltshire woodland. They have two adult children, musician James, and actress daughter Gael who is married to Andrew Lincoln of The Walking Dead fame.
It's a mighty long way from their early gigs at London's Marquee Club in 1968 where Anderson's "bug-eyed troubadour" stage persona quickly caught the attention. The one-legged flute-playing was unplanned. "I used to play the harmonica on one leg and the flute on two, but after a reviewer wrote that I played the flute on one leg, I dutifully started to do it and it stuck," he chuckles.
"I play naked under the cod-piece...I've had to replace it several times. I had a collection but they've all gone. They were in a drawer until about ten years ago and have mysteriously disappeared. My wife denies any involvement...
"My rather sexy stage tights vanished too and they were designed for me by the costumier of the Royal Ballet.
"I check the bins to this day to make sure my favourite t-shirt with a hole in it hasn't disappeared too. I've seen the binmen wearing natty jackets. For all I know they're now wearing one of my codpieces..."
Anderson feels lucky to be in a profession where retirement is not forced upon you.
"We waited Covid out and after a year and a half the show lurched back on the road," he says. "It was much easier than I thought it'd be.
"You go on as long as you're productive and capable. Poor old Pavarotti, even before his terminal diagnosis it was obvious he couldn't perform to that level any more.
"It was the same with Sinatra. I saw him live and he only did 45 minutes, short-changed 12,000 people.
"I think, 'I can still manage two hours, I'll give it another year!'"
Ian's health has been "pretty good for the last five years," he says. "In 2021 I had a bad couple of weeks with a viral infection but it passed, and my COPD diagnosis was overturned in favour of more controllable asthma.
"I have the confidence to carry on doing what I'm doing. I have general health checks every year to see if anything is waiting to creep up on me. I go looking for trouble.
"I'm ready to take bad news on the chin and battle through it if I can. And if not, I can ring around and say goodbye to people."