"Everybody is so guilty," Rufus Wainwright says suddenly and provocatively, while explaining his choice of the words Velvet, Glamour and Guilt, to mark his five-night residency at the Royal Opera House next week. "Everybody feels so guilty that they can't be me," he continues indulgently, before dissolving into impish laughter.
Elton John sang at the venue for charity and Björk fleetingly took to the stage for one night, but Wainwright is the first soloist to be given such a long tenure, something he calls "a serious dessert". For two nights he will be joined by younger sister Martha and father Loudon Wainwright III, before performing his successful Judy Garland tribute concert for two evenings, and finishing with his opera Prima Donna.
The singer-songwriter, 37, was first introduced to opera as a teenager by his mother, the folk singer Kate McGarrigle, who died last year. But his talent as a classical composer has only recently emerged. Already a critically acclaimed pop musician, he has recorded six albums and countless film soundtracks (you may remember his delicate vocals harmonised with British folk singer Teddy Thompson's over deep lackadaisical beats in their version of "King of the Road" in Brokeback Mountain). But when it comes to arias some critics are yet to be won over and he declares vociferously, "You know they say you have to be dead for 50 years for them to take you seriously!"
Since his opera Prima Donna premiered at the Manchester festival in 2009 (initially cancelled by New York's Metropolitan after organisers took fright at Wainwright writing his libretto in French with no English translation), he reveals there have been offers to write another. "If you're going to be a bona fide opera composer you have to really drown yourself in the form and go crazy. I would say I am now waist-high and going deeper. You can't just fiddle, you have to go for it," says Wainwright.
The high-camp title of his residency is a clue to Wainwright's flamboyant personality. He says from an early age opera helped him face his own sexuality and he has spoken of his parents' difficulty coming to terms with having a gay son, yet the operatic chime of melodrama and tragedy with his own life was too strong to ignore. Now content with his homosexuality – his partner, theatre administrator Jörn Weisbrodt, sometimes accompanies him on stage – he does not attempt to hide his extravagant side. As for his bold sartorial choices – the brightly-coloured checked jackets, fitted waistcoats and sweeping frock coats, now trademarks and a fundamental part of his theatrical routine – he offers, "I am gay, so it is a matter of life and death. It is genetically ingrained in my survival mechanisms so I seem to have been bitten by the bug. I have made some good decisions and bad ones, but I just want my biography to be full of weird pictures."
It becomes clear Wainwright is an off-stage wordsmith. He revels in shocking his listener with carefully considered word alloys and similes that undulate off the tongue with surprising ease. Singing on stage, he says, is akin to going into surgery, "you just want the person to live", and he compares his escape from musical injury to the stealthy reserve of a Second World War Japanese suicide pilot, more literally his "Kamikaze physique": "I just jump in there as if it's my last round". You can hear his mind whirring at a remarkable pace that bodes well for his song writing too. Probably his most famous song "Cigarettes and Chocolate Milk", with its familiar "baa bam bam baa baa" piano intro has it: "Playing with prodigal sons/Taking a lot of sentimental valiums/Can't expect your world to be Raggedy Andy/While running on empty with a frown."
And this operatic popstar's world has been far from "Raggedy Andy". Wainwright's autobiographical score gives only a partial insight into the tragedy he has faced. Although steeped in musical talent, the origin of which comes from both mother and father – something he calls "a wealth of genetic instrumentation" – or perhaps because of it, he has battled both crystal meth and alcohol addictions. His mother's death from cancer last year also engulfed him in a grief he made no effort to disguise. A grave sexual assault in Hyde Park aged 14 and his parents' divorce both cast their shadows on the Canadian-American star, the contempt towards his father rehashed in the lyrics of "Dinner at Eight" ("Daddy, don't be surprised that I wanna see the tears in your eyes").
However he seems back on sybaritic form, ready to entertain. Certainly the rift with his father is healing. This is particularly moving when he speaks of their forthcoming performance on stage. "It is always very sympathetic, especially in our family. We probably understand each other a little too well considering half of our material is about each other, so it is an ongoing debate... debacle even," he says. "But in the end harmony usually prevails, and since my mother passed away I have had the chance to perform more with my father, which is turning out to be an interesting new development. There is something about our voices that really melds together well and it is something that I couldn't do before because I was such a mama's boy."
Now his own fatherhood has brought a trickle of calmness amid the clang of tragedy. Perhaps unconventionally, he paired up with Leonard Cohen's daughter, Lorca, to have a child, which was born earlier this year. The couple are not giving any details about how the conception actually occurred. "It is pretty shocking how immediate the human voice, when singing, is to a baby. Maybe it is all babies in general, but you get a sense when you are singing a lullaby to your infant that music is the first language that a human understands," he says of his daughter, Viva Katherine Wainwright Cohen. "It is about transporting the soul through the different dimensions of consciousness and unconsciousness. I highly recommend anyone to sing to their baby. The minute I start singing she is rapt and I don't even think it is my wonderful voice, I think it is this kind of vibration that occurs when a voice is speaking." However, if in the future the grown-up Viva Katherine decides to boycott her ample musical DNA, it won't trouble Wainwright in the slightest. "We are all kind of hoping for some lawyers; there are a lot of musicians and we need some better contracts," he muses.
It will only take Wainwright one memorable record to propel his status from cult following to widespread success and adulation. As busy as he is with operatic projects, fans will be relieved to hear he is not abandoning his more commercial, poppy-rock sound. These days he is working on a new album with slick DJ and music producer Mark Ronson: "I am taking my time because I want it to be right but I want to make something of a pop record." His puckish nature once again resurfaces and with an elfin cackle he adds, "We are definitely courting musically at the moment."
'Five Nights of Velvet, Glamour and Guilt', Royal Opera House, London WC2 (020 7304 4000; www.roh.org.uk) 18, 19 & 21 to 23 July