Hugh Is it a mosquito? Or a dodgy refrigerator? No, that faint whine you hear is just the just sound of a new Coldplay album hoving into view. In the 11 years since their breakout hit "Yellow", four middle-class young men who met at university have become Britain's biggest and blandest band, achieving more than 40 million album sales and worldwide fame along the way – but the more their stature has changed, the more their music has stayed the same.

Niall Biggest doesn't necessarily mean blandest, Hugh. But perhaps you're mistaking over-familiarity with blandness, because Coldplay write the sort of songs that deserve to be played over and over. Unless you've been trapped in a cage for the past decade, you'll know at least two songs from each of their four albums (the fifth, Mylo Xyloto, is out tomorrow). Even if you don't know, you know. "Yellow", "Trouble", "In My Place", "Clocks", "Talk", "Fix You", "Viva La Vida"... I've got big anthems on my side.

Hugh How right you are, Niall: biggest doesn't necessarily mean blandest. It's just in this case we have an act whose success is predicated on vacuity. To wit: Chris Martin's monotonously wistful, quasi-ethereal vocals. The back-of-a-postcard platitudes. And that anodyne mixture of sorrow and uplift, in which each emotion serves to cancel the other out. All of which conspires to make those anthems as offensively inoffensive as they are melodic.

Niall I'm not going to pretend that Chris Martin will be releasing a Jarvis Cocker-esque poetry collection of his lyrics in years to come, but then neither is he. Wistful, ethereal vocals, but also melodic? Sounds to me like you're describing left-field pop music, rather than just rock music – and there's quite a difference.

Hugh Seeing Phill Jupitus take Coldplay to task in a recent stand-up set confirmed there is nothing more uncool than slagging off a band so patently uncool in the first place. But left-field pop? Seriously? Much fuss has certainly been expended on Mylo Xyloto's poppier direction. But what this constitutes, in reality, is some ravey synthesisers and a guest appearance from the ubiquitous Rihanna. It couldn't be more conservative if it came with endorsement from Simon Cowell.

Niall My problem with you is the same problem I have with most of the anti-Coldplay brigade; you sound like you're rallying against people's idea of Coldplay rather than the actual band themselves. Because what I see is what I want from most rock 'n' roll stars, but too rarely get: a neurotic frontman prone to either the pits of self-doubt or the heights of self-regard, sometimes at the same time; bombastic, stadium-slaying choruses; and some faintly ridiculous get-up (have you seen drummer Will Champion's bright pink combats?). All that before we get to the fact that "boring" Chris Martin is bezzie mates with Jay-Z, married to an A-list Hollywood actress and, like, Made Poverty History. Nearly. As for the tug of war between sorrow and uplift, I've heard Mylo Xyloto and it certainly pulled on my heartstrings. "Up in Flames" and "Up With the Birds" are the sparsest, most beautiful things they've done and if you don't get carried away with the overblown majesty of "Charlie Brown", "Major Minus" and "Princess of China", then you're sturdier than the Thames Barrier.

Hugh I'll sob into my Strongbow with the soppiest of them, Niall – as was the case when I saw Elbow at Glastonbury this summer. Now there are some rock stars who give me what I want: their frontman is a born showman and their songs grandly sentimental but grounded in lyrical detail. By contrast, Coldplay were workmanlike, distant and mechanically polite. And though I admire your attempt to melodramatise the workings of a tetchy frontman, I do wonder about equating Chris Martin's allure with his celebrity connections. Or does a fiercely guarded marriage to a wholesome lifestyle guru confer some mystical charisma upon him that I'm missing? As for your Make Poverty History reference, that brings to mind another oft-derided rock star. Say what you like about Bono, but his bombast as musician, activist et al remains formidable. If Martin and Co sang about changing the world or a drunken fumble in the days of yore, I'd be happy. Just no more teardrops being waterfalls as we fly at the speed of sound while lightning strikes, OK?

Niall Ah now Hugh, don't begrudge a man a metaphor. From where I was standing, Coldplay upped their game in every way at this year's Glastonbury. They put their balls on the line – who ever unleashed fireworks at the beginning of their set? If anyone was workmanlike at this year's festival, it was U2, a band so overwhelmed by the sense of occasion that they forgot to put together a good setlist. Not Chris and Co, though; theirs had the necessary ebb and flow of big hits and beguiling new songs. As for Chris Martin, his appeal doesn't hinge on the celeb inner-circle that was looking on at Glastonbury – he's always been a bit barmy, going back to 2001 when he stormed out of the Brat Awards after making a baffling speech about Craig David's hair. But, it does add a nice gloss of international bling; they're Britain's biggest band and that's reflected in the company they keep. Are we adhering to the British archetype when we get so sneery about one of our own doing so well? I mean, at least they still live here. For now, anyway.

Hugh Niall, please believe me when I say that my sneering is driven by sincere contempt: not only for their own musical deficiencies, but for their pernicious effect on a whole generation of British rock musicians. Bands like Keane, Snow Patrol, Athlete and Editors, who have followed their emotive, emptily anthemic example and prioritised bigness over cleverness in their hunt for sales. Only, in recent years, such calculated populism has backfired; rock-music sales have nosedived and, last year, there were a mere handful of guitar bands among the UK's top 100 bestselling albums. Martin and Co may be sitting pretty for now, but, in rising to the top, have they laid waste to the scene from which they sprang?

Niall I'm not sure we should be laying the blame at their door, Hugh. Coldplay emerged from one of the more beige eras of British guitar music. And we shouldn't just think of them in terms of rock music. Coldplay are bigger than that – making pop music, creating songs that connect. I'll wager they'll sell more than all the X Factor contestants combined by the end of the year. And in doing so, they'll inspire a new wave of bands to use their imagination on a grander scale.

Niall Doherty is reviews editor at 'Q' magazine