How do you work against the weight of expectation? “I can’t,” says sufi pop singer Rahat Fateh Ali Khan, comparing himself unfavourably to his uncle, the late Pakistani superstar Nusrat Fateh Ali Khan. “I have a fraction of the artistry he had. He was the Voice – when he sings, he’s in your spirit. I can honour that, but I can’t replicate it. His western audiences didn’t even understand the languages he performed in, but their responses? Mindblowing.”

In PR terms, it seems a car-crash admission; Khan is on course to sell out the O2 arena this weekend for the second time, with a three-hour performance of devotional music (qawaalis), poems (ghazals) and film songs. He headlined the Nobel peace prize concert two years ago, and breezily credits himself with bringing the album format back to life in his native Pakistan. With his numerous appearances on chatshows, judging panels and major film soundtracks, the 42-year-old has built a reputation as the subcontinent’s most popular singer.

Faisalabad-born Khan comes from a family steeped in six centuries of qawaali tradition, but is best known to contemporary audiences as nephew to Nusrat. The latter was a transcendental force who would perform sitting cross-legged on a rug and routinely bring audiences, literally, to their knees. “In our century there have been only one or two voices like [his]”, wrote the critic Geoff Dyer in 1994, “voices that rend the soul even as they soothe it.”

Twenty years ago this summer, Rahat was performing with his uncle on what would be their last US tour together; Madonna and Michael Stipe turned up to their LA shows, Susan Sarandon and Tim Robbins to New York. Massive Attack remixed one of Khan senior’s greatest qawaalis (Dama Dam Mast Qalander) into a dubby club edit; producer Rick Rubin signed up “the master” to his label, American Recordings. Less than a year later, at 48 years old and reportedly weighing more than 21 stone (300lb), Nusrat was dead. Collaborators, including Peter Gabriel and Eddie Vedder of Pearl Jam, lined up to champion his legacy. Rahat, then 23, was expected to quietly carry on the family tradition: a stoic commitment to devotional music. No one expected him to become a blockbuster entity in his own right.

“That journey hasn’t been easy,” he says, looking over the canal from the Guardian offices, “it’s hard for artists to get real respect at home. There is little value placed on what we do.” India, he says, has been kinder, which goes some way to explain the 100 or so songs he has recorded for the film industry there, among his 16-album discography.

“The first song I wrote myself was Sab Jhoote [It’s All Lies]. That was just three years ago, in Manhattan, coming back from a show and fed up with my management and the industry.” Khan switches back and forth between English and Urdu as he speaks. After such disillusionment with the music industry, how does he trust anyone? “That’s the thing,” he says, laughing. “You don’t know who is fake and who is true, who is playing politics and trying to stab you in the back. You’ve got to be careful.” It doesn’t sound much fun. What about actual politics? He must get courted by the nation’s ruling elite, or have an opinion on Pakistan’s political weather? “My responsibility is to the music and the industry. I stay in my lane. You’ve got to keep laughing, greet them politely and play the game. That’s the way to deal with them.”

Khan’s new manager, a former fan who used to promote his US shows, tells me about the team of 15 full-time employees working for the singer in offices in Dubai, Lahore and Karachi, and about the boss’s 12-year-old son being next in line for a stellar career. “He’s so committed, he’s not into [Justin] Bieber like kids his age.” Khan himself agrees: “I was nine when I started training and performing, my son is even more passionate than I was.”

The two bicker a tiny bit about what constitutes a challenge in Khan’s career. “I’m telling you,” says Khan, “the Nobel peace prize concert was easy. It was organised. I came in and did something I had done before to thousands. That was fine.”

So what does daunt him? “I’m not [my uncle], that’s the major thing.” Deferential as he is to Nusrat and keen to project humility, the angst catches ever so slightly in the air. “I need to show myself like him, in art. He has a huge and mega art.” Khan, to my surprise, is first to point out that a career in pop might not be the best way to do that. “But it’s all commercial,” he explains. “All the film stuff is business. Those are the songs I practise for, rehearse for, make money from. Qawaali is the art, that’s in my soul. It’s the ground. Everything else is a passing season – wind, rain, sunshine.”

• Rahat Fateh Ali Khan plays the O2 arena, London, on Sunday.