I keep thinking about Alan Mullery. It's one of those facts that sticks with you, that he lost 11 pounds perspiring for England in the murderous Mexican heat during the 1970 World Cup quarter-final. And at the Garage in London, where Mike Scott is on the fourth of five dates, it feels like Mullery's got nothing on me.

"It's the hottest night yet," Scott says. He might mean the temperature, but he could also be referring to the storm he and his band are kicking up. After the Waterboys split, Scott lost himself and his fans in a Celtic false dawn. But now he's taken his finger out of his ear, strapped his electric guitar back on and convened a bunch of hardened rockers (including the revered former Icicle Worker, Ian McNabb, on bass). The result, though hardly ground-breaking, is, like the title of his imminent album, Still Burning.

Scott once referred to Bob Dylan as the imaginary big brother he never had, and he rests heavily on his Zimmerman frame in post-Waterboys songs like "I Know She's In The Building" and "Edinburgh Castle", and even in the rockabilly psychothrash of the old Waterboys number, "Be My Enemy". But it's all tighter and punchier than Dylan would ever want to be.

The new material seems a shade darker than before (witness "My Dark Side"), even if the latest single, "Love Anyway", is pleasant but unremarkable to these ears (although it must be good because the woman next to me keeps taking out her earplugs to have a better listen). Old material like "Medicine Bow" gets a good kicking, and it's clear that Scott is enjoying himself. His songs are made for two-lane blacktops, driving music in every sense. Apart from the arch, waltz-time country of "Has Anybody Here Seen Hank?" ("Going straight down to hell," he sings), there's no respite, and he builds up to a thunderous account of "Building The City Of Light". The heat's turned up another notch and then he's gone, eyes beaming, sweat flowing.

If the Garage is a trifle on the warm side, the Camden Barfly in London is an overpowering inferno. The culmination of Kerrang! magazine's "Week on Planet Rock", the evening is a violent collision of punk and thrash and grunge - and a few decent songs. To fully appreciate this kind of experience, you have to surrender totally and plunge into the maelstrom. In a venue like the Barfly, which is slightly bigger than my living room, there is nowhere to hide. The chaos is everywhere and the air-conditioning is rubbish.

First up are (sic), the diamond-hard geezers from Dublin who opened for Motorhead last year. It's clear they've learnt a few moves from their mentors, but while their industrial-strength set is not original, it's so tight, so rigorous, so tough, that though (sic)'s provenance is heavy- metallic, they flaunt the spirit of `76. There's even a modicum of gobbing. God, it takes me back.

More up-to-date are Radish, a three-piece from Greenville, Texas, led by 16-year-old Ben Kweller. He calls their music "sugar metal", a neat description: part grunge (quiet verses and hectic hooks), part traditional American guitar rock (Nils Lofgren is a friend of Kweller's dad). What sets them apart is the little detours their songs take, their changes of pace and three-part harmonies, plus a penchant for the odd splash of falsetto.

They've not been around for long, but they already have a following. Afterwards, as Kweller travels the six feet from the stage to the door leading to the dressing rooms, he is mobbed by a small but insistent scrum. Infinitely more interesting than, say (to pluck a name out of the air) Oasis, Radish are a few small steps away from stardom. Despite the name.

Speaking of which, sensitive art movies are not what come to mind when 3 Colours Red take the stage. The MC issues a health warning: "It's f-ing hot in here. Now don't go too mad because someone might get hurt." Naturally, his advice goes unheeded and the madness really kicks in.

The band apparently hate being likened to the Clash, but as they slam into "Mental Blocks", which bears a passing resemblance to "White Riot", it is like being caught in the middle of a seething mob. There's also a whiff of the Sex Pistols, for whom they opened at Finsbury Park last year. That date led to a bidding war which was won by Creation, home of Oasis. But if the Gallaghers think they're tough, they should cop a load of 3 Colours Red.

They're insanely hard workers, Stakhanovites straining at the leash. The three front men, in their black T-shirts and tattoos, are like crazed miners at the coalface, and when they launch into "Nuclear Holiday", the Barfly approaches meltdown. Four songs in, after a triumphant "Copper Girl", bassist and lead singer Chris Vuckovic sinks to the floor, near to collapse, and there's a recess while a tray of drinks is brought on. The group are legendary boozers, apparently, but this time it's pints of iced water they're downing. It might be a drinks break, but this isn't cricket.

By now, we're swimming in a raging sea of sweat. "You'd struggle to play croquet in here now," shaven-headed Gavin from Tolworth bellows in my ear, and on "Sixty Mile Smile", and the encore, Motorhead's "Ace of Spades", the beat and the noise and the passion come together in an explosive cocktail. Make mine a Molotov.

Reading Festival: 3 Colours Red and Radish, today (0171 344 0044 or 0541 500 044)