AC/DC, Hammersmith Apollo, London<br></br>Relaxed Muscle, Trash, London

Hell's highway meets Hoxton High Street

If you could melt rock'n'roll down with a spoon and a Bunsen burner, what would you get? What essence would remain? Here's one answer, and it's two middle-aged men in flat caps, one of them screeching about sex in a voice that sounds like a constipation sufferer straining on the toilet seat, and the other dressed as a schoolboy even though the last time he saw the inside of a classroom, the textbooks probably still hadn't assimilated Darwin's theory of evolution. (Another answer, equally valid, would be The Ramones, but they aren't around to argue the toss.) Tonight's AC/DC show is dripping with significance. In the short term, there's the fact that the Apollo is tonight being relaunched as a standing venue - a proper rock venue - with the downstairs seats ripped out. More historically, this is the place where, 23 years ago, AC/DC - having regrouped after the death (in nearby King's College Hospital) of original singer Bon Scott - ended their first tour with Scott's replacement, Brian Johnson.

There's a palpable thrill in knowing that the five men onstage tonight are the same line-up who played that show, and the metronomic tick-tock-tick-tock which announces the gargantuan riff of "Back In Black" is the cue for a sea of satan signs, and you know that a lot of men (it is, to be honest, a very male crowd) are fulfilling a lifetime's ambition by being able to bellow "ANGUS! ANGUS!" over the demonic opening riff of "Whole Lotta Rosie".

The heroic exploits of our own Hawkins brothers - present in the crowd tonight (and their Aussie/ Geordie forerunners will apparently return the favour by watching The Darkness's show here tomorrow) - may have created a renewed appetite for this stuff, but it hardly ever went away. The affection with which the 'DC are held is unique within rock, and stretches far beyond the world of heavy metal. Even in 1977, when rock dinosaurs were being slaughtered left right and centre, the punks appreciated AC/DC's unapologetic, primal brutality, their gonzo three-chord simplicity (not that far removed, in truth, from the aforementioned Ramones).

Yes, they were sexist, but in such a cartoonish way that it was surely impossible to find them offensive. If there's a funnier opening verse than that of "You Shook Me All Night Long" - an absolute joy to scream along with tonight - I'd love to hear it: "She was a fast machine, she kept her motor clean/ She was the best damn woman that I've ever seen/ She had the sightless eyes, telling me no lies/ Knocking me out with those American thighs."

Angus Young, balding, sweating like a melting waxwork under the spotlights, perpetually chewing invisible gum, is as bizarre a specimen as always. Back in the day, of course, he wasn't alone in his choice of stagewear. After Bon Scott dressed up as a schoolgirl for a TV appearance, complete with blonde wig, the group were banned from Australian television. During "The Jack", a 12-bar blues number about Bon catching crabs of the non-marine variety, Young stripteases out of his Molesworth clobber to reveal a pair of Union Jack boxer shorts.

Johnson, too, is an odd little fellow: a bulge-eyed Andy Capp with an almost impenetrable Newcastle accent, introducing virtually every song with "Eere's anuther won for ye, lads". When Angus nicks Brian's hat, revealing a bald pate, nobody falls over in shock. There is something oddly satisfying about knowing that the guardians of the spirit of rock'n'roll are two such unsexy, uncool-looking blokes.

AC/DC retain an admirably pure, give-the-people-what-they-want ethic, delivering a set packed with crowdpleasers like "Dirty Deeds (Done Dirt Cheap)", "Thunderstruck", "Rock'N'Roll Damnation", "If You Want Blood" and the ultimate expression of rock'n'roll nihilism, "Highway To Hell". The one recent tune shows that their cherishable childishness has never left them: "I was born with a stiff... Stiff Upper Lip!" The very Seventies light show is equally straightforward: nothing fancy, just several columns of tri-coloured gels, such as one might see on the sleeve of a live album by Queen or the Lizzy. When they do bring out some props, they're refreshingly literalist. "Hell's Bells"? A giant bell, of course. "For Those About To Rock (We Salute You)"? Why, a tinnitus-threatening salute from four actual cannons.

Leaving the Apollo after DJing the 'DC's aftershow party (weddings, funerals, corporate hospitality: try me, I'm great), the cannon fire still ringing in our ears, we see a man on a stepladder, removing the letters AC/DC from above the door, and replacing them with "The Darkness". The changing of the guard.

Jarvis Cocker takes the Trash stage in fluorescent zombie make-up, a skeleton suit, and a tennis player's towelling headband which makes him look like the Luke Wilson character in The Royal Tenenbaums after an (even worse) nervous breakdown. Except this isn't Jarvis Cocker. If we're inclined to humour him, we're meant to call him Darren Spooner, the Screaming Lord Such-like alter ego in which he fronts his new band, Relaxed Muscle.

I first saw Jarvis Cocker perform these songs in the Royal Festival Hall, under his own name during the last days of Pulp, on the support bill to Lee Hazlewood. That night he seemed lost, directionless. A lot has changed since. The attempts to sound badass ("I rule my woman with a rod of iron") still occasionally sound laboured, but Relaxed Muscle's brutal tales of sex, drugs and violence have a sharp edge.

The dominant sound is Suicide and Cabaret Voltaire, or, to cite more contemporary comparisons, A.R.E. Weapons (with whom Jarvis has connections), and The Fat Truckers (unsurprisingly, since one of their members, Jason, is the other half of Relaxed Muscle, under the alias JP Buckle). At other times it's Antsy drum rumble ("Muscle Music") or Glitter Band glam ("Beastmaster").

Jarvis being Jarvis... I mean, Darren, he cannot help his raconteur tendencies. Speaking through a voice box of the kind used to protect the identities of rape and child abuse victims on television, he tells a series of appalling jokes ("I went to a Greek restaurant last night, things got a bit meze. I saw David Blaine... that guy's out of his box"), encourages us to chant "Don-Cas-Ter!" and rambles about designer jeans being made in the same factory as supermarket ones, but with different labels sewn on.

There's a whiff of Hoxton in-joke about the whole thing - Relaxed Muscle will never unite the nation, never headline the main stage at Glastonbury - but a great songwriter cannot help but write great songs. The final two tracks on the Relaxed Muscle album, A Heavy Night With..., have arresting opening lines to match that of, say, Pulp's "Razzmatazz". On "Battered", it's "I was the smartest kid on the block, but then I got battered". On "Mary", it's "Mary, I just called to tell yer... that both our children are on drugs." For all Relaxed Muscle's qualities, Cocker/ Spooner seems to have happily traded national significance for metropolitan hipness. Perhaps the latter, and not the former, is what he wants right now. A genius on holiday.

s.price@independent.co.uk

Relaxed Muscle: Barfly, London NW1 (020 7691 4246), Fri