For most classical singers, choosing a duet partner requires meticulous scouring of operatic talent. It does not usually involve trawling through a back catalogue of Seventies rock heroes.
But then Alfie Boe has never followed the path of most opera singers. The English tenor's latest musical collaboration is with Led Zeppelin frontman Robert Plant, with whom he has recorded a song on his latest album. A long-time fan of Plant after listening to Zeppelin as a teenager, Boe took the chance to accost him about the project after a chance meeting in a bar in London's Soho.
He is still pinching himself that Plant agreed. "He's in my phone as 'Rock God' and whenever he phones it plays the 'Immigrant Song' ringtone," Boe gushes. "I plucked up the courage and asked if he'd be interested in dueting a song on my new album, Song to the Siren. When we recorded it, I couldn't believe I was stood three feet from Robert Plant screaming into a mic. I love my rock music and I'm a big Led Zep fan. I think that's probably something else the opera world can't recognise."
Boe is weary of the opera world's opinion of him. Despite appearing on most of Britain's major operatic stages, from the English National Opera to the Royal Opera House, he has never felt fully accepted by the classical establishment.
The 38-year-old believes his peers looked down on him from the moment he was chosen to play the lead in Baz Luhrmann's Broadway production of La Bohème. Born in Fleetwood, Lancashire, he was the youngest of nine children and was working as a car mechanic when he discovered a love for singing in karaoke bars. As his popularity grew, so, too, did the disdain of the traditionalists who found his screaming fans and hit records somewhat vulgar.
He caused horror among opera aficionados earlier this year when he told Radio Four's Desert Island Discs that he found opera "boring" and never went to see it. A number of leading figures in the classical world criticised him.
Award-winning opera director Sir Jonathan Miller was one of the first, saying: "If Alfie Boe thinks opera is boring then it's very odd that he's in it at all." That comment upset Boe, who had worked with Miller just months before. But far more wounding was Miller's pay-off line: "I know he comes from something other than opera: he was a car mechanic, I believe."
It summed up what Boe had known for a long time: in the stuffy world of classical music someone from his background never fitted. "They can't take any criticism, the operatic world," he said. "I basically said something that is plain obvious to a lot of people: opera is boring. It takes a really good production to make it exciting and sometimes they don't cover that."
Boe believes such criticism would not have been levelled at other opera singers more in tune with the establishment. "I think it was a bit discriminatory," he said. "If Antonio Pappano had said it, or even if Jonathan Miller had the nerve to say, 'There are productions out there that I cannot stand watching because they're so boring', they would have been seen differently and taken with an element of respect. But, because of my background, because I came from a working-class family and used to be a car mechanic, they had a dig. I've had so many stabs before, I could leak all over – but I don't care. There are a few more spots to hit first."
Despite his reputation for bluntness, Boe is disarmingly mild-mannered in person; his soft Lancashire speaking voice betrays little hint of irritation.
In truth, he enjoys the role of enfant terrible: "I quite like being known as the bad boy of opera. I think I ruffle some feathers but only for the right reasons. I hate injustice and I like people to be treated fairly and equally. I don't believe in the class system of the operatic world."
Boe is unlikely – still less so while burdened by such memories – to mellow any time soon. "The music has always been the thing for me, but sometimes the way that you're treated can be a real insult," he says.
Despite this, he says he intends to continue singing opera, while developing pop music on the side. "I'm nowhere near finished climbing the ladder for where I want to be. There are loads of people I'd love to sing with: Bob Dylan, Stevie Wonder, David Bowie."
And he will do all this despite it offering further fuel to his stuffy critics? "Yeah," he says. "Boo-hiss to the opera establishment."
Boe's new album Alfie is out on 31 October on Decca