"AIIIITICCHOOOOOW!” The sneeze ricochets off the mike stand before disappearing, damply, behind the drum riser. Roadies wince. Guitar techs flinch. The culprit - a middle-aged man with a pyramid of flammable blond hair - sniffs sheepishly. Fumbling in the pockets of his distressed denim jeans, he extracts a wad of tissues and proceeds to dab his streaming nose. “Bloody hell,” snuffles Joe Elliot, by way of apology. “That were a big 'un.”

As with the sneezing, so with the rock. When Def Leppard fall ill, they do so with the brio you'd expect of a band so enamoured with the pageantry of stadium rock they used to be deposited onstage in laundry baskets. Two weeks into their world tour, the diamond-selling soft metal warhorses found themselves flattened by an upper respiratory tract infection. X-rays were undertaken. Sick notes were scribbled. Pyjamas - possibly distressed denim pyjamas with tiny diamante semi-quavers - were donned. Now, just days after they were given the all-clear, a sneeze-punctuated soundcheck at a glumly utilitarian amphitheatre on the outskirts of San Diego does not bode well for a still-poorly Joe Elliot. Does he want to get rocked? He does not. Frankly, the 48-year-old singer would rather be tucked up on the tour bus, sucking a lozenge and watching Dalziel and Pascoe (“I love Dalziel and Pascoe!”). But the die is cast: 20,000 Californians have ensured that tonight's gig is a sell-out and the show must go on.

Elliot, understandably, is concerned. “I've just had a steroid injection in my butt,” he rasps, wincing as he manoeuvres into a folding chair in the concrete garden that serves as the venue's hospitality area. “It bloody hurts, but what can you do? We can't afford to cancel. I mean, just blowing out them shows we did (six North American concerts have been rescheduled) has turned this into the most expensive cough in rock'n'roll, hurr-hurr!”

The band was formed in 1977 by Sheffield teenagers Elliot and Rick Savage, and swiftly joined by 15-year-old drummer Rick Allen. The ineffably polite guitarist Phil Collen came on board in 1982, followed by affable Irishman Vivien Campbell, who was recruited after the alcohol-related death of the guitarist Steve Clark in 1991. From the outset they found themselves heralded as standard-bearers of the so-called New Wave of British Heavy Metal: a state of affairs that Elliot - a man not overly convinced of the merits of subtlety - considers “crap. We have tried to explain to people for the last 25 years that we're not a heavy metal band,” he sniffs.

Nevertheless, the notion persists that Def Leppard belong within the same leathery parentheses as Iron Maiden. A case of you-say-tomato, perhaps? “Bollocks,” counters the carbuncular frontman. “We always had a foot in pop. But then, some people still think we're American. Some people think we split up years ago. You just try to get on with things and hope everyone else will catch on, really.”

Time may have withered their once voluminous perms but it has proved beneficent to the Leppard muse, which, as the sporadically excellent new album Songs from the Sparkle Lounge is at pains to point out, is as attuned to the giddy, harmonic rush of arena-orientated Pop-Rock FM as it was back in the days when it was considered acceptable practice to release a song entitled Let's Get Rocked (“I suppose a rock's out of the question?”). Now, after years of critical derision and dwindling sales, a comeback is on the cards. Songs from the Sparkle Lounge entered the UK album charts at No10. Much of the British leg of their world tour has already sold out. Cynicism seems to have been replaced with an increasingly less grudging affection for their middle-aged antics.

“If you come through that cloud on the other side, I think you gain kudos for just surviving,” Elliot says. “And then people listen to your music differently because you're still around. A music career is like a wheel. As long as it keeps moving, the bit that's got ‘success' written on it ends up back at the top. You hope.”

Backstage, the pre-gig mood is relaxed. To our right, Vivian Campbell lifts weights (“Oh Christ!”) while reclusive guitarist Rick ‘Sav' Savage - the sole remaining bearer of a mid-Eighties bouffant - quietly signs a guitar for a local charity. To our left, a shockingly muscular Phil Collen is slurping camomile tea. Over by the giant potted palm, the drummer Rick Allen - who famously lost his left arm in a car accident in 1984 - discusses his interest in the obscure Indian discipline of Deeksha with their tiny tour manager (“I experienced the totality of the human condition. And it was horrible...”). It's like a coffee morning with the Dad's Army cast.

“Everyone's gorra get old,” barks Elliot. “What we do is extremely physical. Can you imagine someone of 48 in the Premiership? We're still in the Premiership. But you've gorra be sensible if you want to stop it from falling apart. Diet's the thing,” he confides. “I had a bowl of soup when I got here.”

Tonight, Elliot's bronchial rasp fails to dull the timeless lustre of Def Leppard's back catalogue. Adolescent boys in Pyromania T-shirts hop from trainer to trainer, housewives wave Union Jacks, and elderly men with shorts buckled around their chest roar along to such bittersweet soft-metal belters as Love Bites, Pour Some Sugar on Me and Armageddon It.

It's an hour after the band has clambered, sweating, offstage, and Elliot's thoughts are turning to the future. “In five years time I'll be 53,” he croaks. “Will we still be together? Yes. I mean, I don't know whether it's because we're scared shitless of things falling apart. We come from a working-class background where [adopts old-man Yorkshire drawl] ‘You've got one chance, son, take it while you can or you're back to the factory.' So this [he gestures to the empty stage] becomes the Holy Grail and you've gorra cling on to it, baby. But if it all fell apart tomorrow I'm not gonna burst into tears. I'd look at it and I'd go, ‘Well, we've won.' Because we got this far. And that's way further than most. I mean, what's better than rock'n'roll?

“Exactly,” he says behind his sunglasses. “Nothing.”

Def Leppard's UK tour starts at the SECC Glasgow on Jun 17 (www. deflepparduk.com 0141-287 7777)

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