A couple of months ago the comedian and lyricist Tim Minchin told an audience at a literary festival: “I hope my daughter dies tomorrow in a car crash. I’ll tweet if she does.”

That sounds bad, out of context.

“People get dim about stuff sometimes,” he says of the ensuing outcry. At the festival, he explains, he was trying to illustrate his point that you can’t actually “tempt fate”.

“You have to overcome your superstitions. Saying ‘I hope you have a plane crash’ isn’t going to change the outcome of a person’s flight. I said, 'I hope my daughter dies tomorrow at 10am.’ The specificity’s very important. You have to say something that won’t happen - because of the odds - in order to overcome your superstition that it will happen. "You have to overcome your megalomaniacal 'I’m so important’ human bullshit bias - you have to overcome the idea that you are magic. Because you’re not magic.”

Minchin is magic, though. He’s the most famous Australian nobody can quite picture until you say “that ginger bloke with the piano and the funny songs”.

And they are very funny. Look up Prejudice on YouTube - a song about how six little letters (N, I, E, R and two Gs) can be so hurtful. Millions already have. Or Lullaby, his wry assessment of fatherhood (“Your blanket’s hand-knitted, with pure angora wool/Your nappy is dry and your tummy is full/Of enough antihistamine, to chill out a bull/Yet still all this gringing”).

Through his twenties, he was an impoverished jack-ofall-arts playing late-night gigs in “bars full of drunken British tourists in Melbourne”.

The combination of music and comedy - he says he’s funny for a musician and a good musician for a comedian - held him back. No one could see a market. He was advised to specialise in one or the other but he wouldn’t. “I was having too much fun,” he says but also, he’s stubborn. Most people would have chucked it in and become an accountant.

Eventually, YouTube happened (“it made me”) and Minchin went viral. He toured. He made DVDs. He became that ginger guy with the eyeliner (to exaggerate expressions) and the backcombed hair (umm). We started calling him British-Australian rather than just Australian (he was born here to Aussie parents and lives here now).

At the same time he was reading lots of philosophy and his unflinching rationalism became a trademark. A Richard Dawkins, but funnier, nicer and camouflaged in flowery piano trills. One Minchin song re-examines love at first sight with the opening couplet: “You grew on me like a tumour/And you spread through me like malignant melanoma”. Another rejoices in Christmas as a time for humanism rather than deism.

Yet another, Ten-Foot Cock and a Few Hundred Virgins, considers God and anal sex.

Why is he still not quite known? “To be a household name, you have to be on telly,” he says. “I don’t believe comedy songs work on the telly.”

Minchin might just be too risque for mainstream television.

Last year, ITV cut his song Woody Allen Jesus from the Jonathan Ross Show because, “the tone wasn’t quite right for the Christmas show”.

True, he did liken Jesus to a zombie. He also covered the virgin birth with the memorable verse: “Breeding without the opposite gender is commonly known as parthenogenesis/Other animals that don’t need males include a lot of lizards and various snails”. But still, you would have thought a television audience could take a bit of mild blasphemy.

ITV thought not.

Critics then accused him of picking only on Christianity. Was he scared of taking on Islam? “It’s a non sequitur,” he says now. “It’s like saying, 'Why are you doing jokes about ice creams, not dolphins?’ "I have no obligations to be balanced, I’m a comedian. Secondly, Christianity’s my culture, it’s the culture I grew up with. I don’t really want to criticise Islam. I mean, I do it but it’s not my thing, even though I do spend five minutes on stage with a Koran talking about sacredness. Thirdly, sure I’m scared of stirring up a violent minority and getting my family killed. Is that not a good reason? It’s like saying, 'You punched that tiny guy, now go punch that karate guy’.”

What we are supposed to be discussing here is Jesus Christ Superstar. Minchin is taking a lunch break from rehearsals at 3 Mills Studios in east London. Alongside Chris Moyles’s Herod, God help us, and Mel C’s Mary Magdalene, he will play Judas Iscariot in the stadium version of Andrew Lloyd Webber’s 40-year-old hit next month.

This seems an odd career move. Still basking in the huge success of Matilda the Musical, first in the West End and now Broadway too, Minchin has been variously hailed as the “saviour of British musicals”, “an original talent”, “a unique genius” and “unmissable”. But now he’s doing Superstar. With the “saviour of Radio 1”. And a Spice Girl. And Lloyd Webber. Not exactly cutting edge.

“My interest is this incredibly told story - The Passion of the Christ put to rock music,” he says. “As a lover of Deep Purple and Seventies rock, I’m interested in the show musically.

As a musician and a fan of Tim Rice, I’m interested in it lyrically. And as a child whose life was changed by Lloyd Webber’s Starlight Express, why would I ever not do this? "It’s theatre. It’s a story. I have no problem delineating stories from real life. I get really annoyed at people who call themselves psychic and telekinetic, but Matilda does magic with her eyes. I tell my children all sorts of fantasies but it doesn’t mean I’m trying to sell them something as truth; it’s just stories.”

To progress further, we must separate the two Minchins. Minchin One is the passionate advocate of humanism and Minchin Two is the happy-golucky storyteller. Of course they are intertwined, but they don’t always both define him. He’s doing Superstar because he wants to. And it will make him more famous, because there’s also a third Minchin, the one who wants affirmation.

“Fame is like group sex,” he tells me confidently. “You desire it till you’ve had it and then it’s like 'meh’.”

I’m halfway through admitting I wouldn’t know on either count, but he interrupts.

“Actually, that’s a bad metaphor.

Once you’ve had group sex you just want more group sex, but I really believe most of us are driven most of the time to be affirmed. I’m absolutely driven to be affirmed but I’m not driven to be affirmed by being rich and famous. Although they are intrinsically linked to what I am driven to be affirmed by, which is impressing people.”

This is how he talks. And writes lyrics. An idea wrapped in the opposite idea inside a riddle. On Twitter he describes himself as “a musician with a swollen sense of my ability to articulate my insignificance”.

He also calls himself an “educationalist”.

Minchin One, the advocate, wants to expose the hypocrisy of those who preach morality but don’t practise it.

Does he believe in nothing? “I’m a humanist materialist.

I don’t believe in anything that’s unlikely. To believe in Jesus, you can either make the assumption that there was a man who broke all the laws of biology and physics or say that humans have mythologised other humans throughout history, and sometimes myths take off. Just because ideas take off doesn’t mean they’re real.”

He continues: “I’m going to write a musical with the Pope as the central character. I want to take a sympathetic view of what it would be like for a young man - while other young men are getting stupid tattoos or accidentally getting girls pregnant - to say 'I believe in a master of the universe’.

What are the odds that these young men stick with their beliefs? That they won’t, at some point, think, 'Well, I don’t really believe that shit any more but this is the structure within which I do my pastoral care. I’ve got bills to pay’?” Last scene: an atheist running the church. Curtain falls. There would be protests. ITV wouldn’t like it. But the lyrics would be good.

Until then, we have Tim Minchin playing the questioning, betraying disciple at the O2 arena. It’s a long way from the Melbourne dive bars, but it sort of adds up. It could even be part of a grand design.

“No, it’s just luck,” he says.

“There’s no soul, no nothing.

It’s just luck.”

And with that, he heads off to rehearse Judas.