James McCartney, Hoxton Bar and Grill, London

In profile, he has his dad's pursed mouth and nose. Full on, the face becomes more eerily identical the more you stare at it. No DNA tests would ever be needed to confirm that this is indeed Paul McCartney's only son, playing his first official London gig at the age of 32. Start listening as well, though, and the fantasies that intrude aren't of the Beatles' Shea Stadium triumph, or Abbey Road genius. I start to imagine Paul McCartney's Liverpool suburban upbringing shifted in time to the early 1990s, with him now listening to Nirvana and the Cure, not Elvis Presley, at night, and instead of conquering the world, remaining a talented, almost content weekend rocker, sometimes musing what might have been: McCartney, in other words, if the sparks of genius and luck never struck. That seems James's honourable level.

Of course, the good fortune which let James grow up observing Paul at first hand is countered by the curse of being compared, not to some other beginner, but one of the 20th century's best. Great rock stars' offspring are seen as royalty once was, as direct replacements, even reincarnations, of their gilded parents. Julian Lennon's resemblance to a callow John made him a minor pop star in the decade after his dad's death. Sean Ono Lennon's mixture of mother Yoko's avant-garde path with dad's pop nouse has made him a well-liked associate of Beck and the Beastie Boys. But only Zak Starkey has equalled his famous father Ringo, becoming a highly respected drummer for the Who and Oasis. Don't put your son or daughter on the stage is sound advice for any Beatle.

James followed this course for many years. Compared to sister Stella, he was the Quiet One of Paul's children, but generally living the normal life Paul had intended when sending him to the local comprehensive near his Sussex home. He supposedly sometimes changed his surname, determined to make his own way. His first mention of Paul tonight mixes embarrassment and acknowledgement. "My dad gave me this guitar," he murmurs before "Glisten". "I Love You Dad" makes his bond even more naked. He has co-written three songs on recent albums by Paul, who is helping on James's own upcoming debut.

James's voice resembles Kurt Cobain's gravely whine and hollered yelp on "Mix", and the Smashing Pumpkins' glammy end of grunge is also prevalent. He dutifully lists his roots –"This one's highly influenced by the Cure and Neil Young" he says of "Glisten" – and the results combine the early 1990s rock on the radio when he was a teenager with bright 1960s arrangements. He switches from guitar to keyboards, then mandolin, and has a strong voice when he rocks out. But only on "Wings of Lightest Weight" does he sing softly with success. His shy inexperience is to be expected, but the music is that of a hopeful rock band 15 years ago; the fault of this 32-year-old delaying his ambitions. He leaves the stage with a familiar, bashful Macca grin. You can't help looking forward to the fuss over this decent young man with Beatle blood falling away, so he can play happily to whoever really wants to listen.