I arrive for my rendezvous with Toby Spence strongly expecting him to wash his hands of the silly mug he is preparing to play on stage at the Coliseum. After all, the hero of Bernstein's Candide is the archetypal naïf, the simpleton from hicksville who maintains his belief in the “best of all possible worlds” even while acts of unspeakable cruelty are unfolding all around him.

Spence, meanwhile, is growing up. The English tenor is no longer opera's blue-eyed boy, much more the grizzled veteran who is only interested in hard graft. “I'm less boyish than I used to be,” he says, “and I mean by that that I won't be pushed around any more.”

So, why the dopey Candide? “It would be fair to call Candide naive, but there are two reasons why I don't. One is that to play a role right you should always find a way of respecting it, and the second is that playing his story as an idiot is just not very interesting. In the end, he draws his own conclusions - he says that there is good and bad, pure and evil in the world, and he learns this through experience. He's thrown into a world that's very cruel, and in the end experience teaches him to draw another conclusion.”

To say that Bernstein's 1956 adaptation of Voltaire's novella has had a troubled history would be an understatement. Conceived to run on Broadway, the show's awkward mix of political satire and comic vaudeville has always struggled to attract a commercial audience, even after Bernstein made numerous revisions, and several more writers (among them Stephen Sondheim) were brought in to redraft. Since then, Candide's usual berth has been the opera house, though a stylish National Theatre revival by John Caird in 1999 (with Simon Russell Beale as the insufferable philosopher of optimism, Dr Pangloss) made an argument for Candide as a cogent - if rather frothy - musical.

But English National Opera's Candide, staged by the American director Robert Carsen and already seen in Paris and Milan, promises us a more radical reboot. “The [Bernstein] foundation has given Robert carte blanche to do what he wants with the book, which they haven't given to anybody else ever,” Spence says. “He's really picked up the ball and run with it.”

What emerges is a Candide with Bernstein's angry liberal conscience ramped up to feverish heights. Dr Pangloss teaches his empty rhetoric at the White House, not in Westphalia, but - geddit? - West Failure. A quartet of world leaders, among them Dubya and Tony Blair, cavort in their underpants. Come the fearsome auto-da-fé scene, says Spence, and “it's the Ku Klux Klan, the McCarthy hearings. Pangloss and I are hanged; it's a nasty scene - these are things that are going to shock.” Indeed, at La Scala, Milan, a disrespectful reference to Jesuits had to be deleted on pain of cancellation.

Spence obviously can't wait. He thrives on Carsen's brand of aggressive theatricality, and is keen to work with stage actors (Alex Jennings plays Pangloss). “Every day I see him adding something, or taking something out. Whereas we opera singers arrive having made a lot of decisions, he's putty, and that's fascinating for me.”

That's all part of the Toby Spence rebrand project, as he shifts from being the dreamy, tousle-haired love interest to characters with more bite. “Roles choose you, really,” he says. “And a lot of those roles tend to be Ponce Charming. So it's great to have a story with a little more grit. But you need the age, you need the experience and you need to the stage time to to make it worthwhile.”

A fair amount of soul-searching lies behind that credo - the reason, perhaps, why Spence's most important new role is the dissolute playboy, Tom Rakewell from Stravinsky's The Rake's Progress, which he sang in Paris and will take to Covent Garden in a couple of seasons when they reprise Robert Lepage's glitzy production. For while Spence's path to opera singing - a choral scholarship at Oxford, then Guildhall, sounds smooth - it felt bumpy to him. “I used to battle to lead a rather sort of split existence, and be the person I was brought up to be at home, and then the singer at work - it doesn't work. It's a selfishness, and it's a strangeness that I've had to learn.” An early casualty was Spence's first marriage. “I was still a student, and suddenly I became a singer, and I had a bit of money, and I also wanted to explore myself, the world ... well, I've said it before, the Rake is a role that's made for me. So big apologies to my ex-wife.”

Now he's more sorted - though the private life doesn't seem quite under control yet. Last year Spence had planned to marry his partner, the Spanish actress Barbara Lluch, before he called a time out. “I took an executive decision,” he says, looking sheepish. “We struggle on as a result of that.”

The truth is that the singing comes a definite first - and Spence is not afraid to throw his weight around. “You need to fight in order to make the piece worthwhile. You need to fight with yourself, and the director if you're not getting what you want.”

It's the gospel that's keeping Spence sane - even when he plays a Tom Rakewell whose downward spiral will always end in Bedlam. “The message of that one is that you can go mad,” he says. “And that's scary. But I think I've managed to put things into play that will stop me going mad - even though I have followed a pretty similar path.” There's a nervous chuckle: call it an overstatement perhaps, but this Candide is certainly no innocent.

Candide, Coliseum, London WC2 (www.eno.org 020-7632 8300), from Mon

Editor's choice

• Live fast, die young: The 27 Club
• Madonna's 50 most memorable moments
• Proms Podcast with Pierre Boulez