CHEER UP, Tjinder! I know that nothing spoils your day quite like having a No 1 single and a rhapsodised, gold-selling album after years of destitute obscurity, but you could at least try to look cheery. Couldn't you?

Well no, apparently not. Tjinder Singh, writer, producer, acoustic guitarist and lead singer of Cornershop, was so glum and disengaged throughout the band's set at the University of London Union on Wednesday that you'd think he'd just released a commercially disastrous squawl of cacophonous agitprop. Whereas, in fact, he hasn't done that for years. Opening the show with "Sleep on the Left Side", an easy groove with accordion chirrups, he stood stockstill, arms by his sides, as if he were facing a firing squad. If only we'd realised then how lucky we were. Perhaps fascinated by the film montage of breakdancers and bellydancers on the screens behind him, he spent most of the rest of the gig not facing us at all.

This gloominess was inappropriate on two counts. First, because life is so sweet for Cornershop at the moment, and second, because their music is now so positive and playful. Renowned in the early Nineties as "John Peel student crap", to quote an acquaintance of mine, Cornershop have evolved almost beyond recognition. Hear "Brimful of Asha" - the original version or the Norman Cook remix which propelled it to No 1 - and you might question what all the ballyhoo is about. Hear it a second and a third time (which can be achieved by listening to any radio station in the country, including Radio 4, for an hour) and the bloody thing'll be stuck in your head like grit in a contact lens.

The other songs on When I Was Born For the Seventh Time (Wiiija) are very similar and very different. Cornershop subscribe to the Lou Reed theory of rock'n'roll: two chords is pushing it and three chords is getting into jazz. Even the so-called country song, "Good to Be on the Road Back Home Again", follows the simple pattern of relaxed, clean guitar strums over a funky beat. What gives the album its rainbow of colours is the way these basic elements are embroidered with sitars, tambouras, scratching, synths, samples and a Casiotone keyboard not seen in the shops since 1983.

It's a precariously excellent record, ie, it's excellent but it's on the verge of being no good at all. The experimental grooves have only just enough style to elevate them above stoned studio tinkerings; Singh's mellow singing has only just enough character to stop it sounding like someone sightreading from a lyric sheet. Maybe it's this carefree air that makes When I Was Born ... so infectious, but it is, as I say, a close run thing.

The same goes for the concert. The drummer had to come up with a bandsworth of enthusiasm singlehandedly, but after a half-hearted plod through their Punjab translation of "Norwegian Wood", his colleagues come to life in time for some spiralling psychedelic hazes, far more warm and fluid than you'd expect from a group who once considered musical competence to be a luxury. They closed with an extended "Jullander Shere". It was just on the right side of the hypnotic/stupefying border, although it would have been appreciated more in a club's chill-out room than at a pop gig. And when the crowd realises that Cornershop aren't returning for an encore ("Brimful of Asha" was the fourth song of the night), making the 17-minute "Jullander Shere" a quarter of the entire set, you can't really blame people for booing. Quite a few of them left looking almost as glum as Singh.

At London's Conway Hall on Monday were two bands responsible for some of this year's most archetypally rock'n'roll moments. Rock'n'Roll Moment No 1 came from Dawn of the Replicants, whose fascinating collision of melody and discord would remind you of a sci-fi zombie film, even if you didn't know their name. At the end of their set, the guitarist tried to dismantle his instrument by assaulting it with a drumstick, before realising that a more efficient method would be to use the stage. It was the first time in my long and illustrious concert-reviewing career that a guitar with its neck snapped in two has landed a metre away from my feet.

Rock'n'Roll Moment No 2 was more of a tableau, courtesy of the headliners, Ultrasound. The drummer's got his shirt off, the synth player headbangs so vigorously that he nearly brains himself on the keys, the guitarist runs through all the jumps and windmills he's learnt from Pete Townshend, and the peroxide bassist, Vanessa Best, who may have modelled herself on Myra Hindley's arrest photograph, slumps against the singer-guitarist. He, finally, is Andrew "Tiny" Wood, 34 years old and not far off 34 stone, sporting family-sized tartan trousers and a glittery jumper. I can say without much fear of contradiction that he doesn't look like anyone else in the pop world.

When they're not being called the best new band in the country, Ultrasound are called a prog-rock band, but the label carries derogatory connotations that don't quite apply. True, you shouldn't start listening to one of their tracks if there's somewhere else you have to be in half an hour, but Ultrasound don't write long songs because they want to show off their years of classical training: they do it because they want to construct dynamic, Bowiesque, stately-but-sleazy rock'n'roll epics. And remarkably often, they succeed. The finale, "Everything Picture" sounds like Jarvis Cocker covering Pink Floyd's "The Great Gig in the Sky". Strobe lights flash. Flurries of confetti flutter over the audience. No really, it's not prog-rock. I promise.