Of all the many brilliant and quixotic talents to emerge out of the punk era, Joy Division have proved to be easily the most influential. Bono has admitted the enormous debt U2 owe to their Mancunian forefathers. Every important act from Jeff Buckley to the Manic Street Preachers has lent an ear to their tunes: more unlikely but intriguingly, Joy Division's Closer is apparently George Michael's favourite album. Without Joy Division, there would have been no New Order (the JD's regrouping after the tragic suicide of Ian Curtis), but the shape of modern music would have been entirely different... almost unthinkable.

   Although Joy Division were by no means the first band to come out of Manchester, they were the first to be given the tag "Manchester band", as if it was something very special, and indeed it was. While punk either burned itself out or headed in other directions around London, Joy Division's isolation in Manchester - where, back in the seventies, record companies feared to tread - assisted them in creating a new sound and identity that transformed the form and content of rock music, shifting it towards dance culture with the heavy, hypnotic rhythma of songs like Transmission, and into unparalleled levels of insight and introspection courtesy of Curtis' brilliant lyrics. Since then, there have been countless "Manchester bands", and almost all of them have either taken from Joy Division (James, A Certain Ratio), or reacted against them. (In some cases both, as in The Stone Roses, The Fall, Happy Mondays and The Smiths, whose Morrissey initially declared he wanted to cast some colour in the "greyness" cast by the revered band. Later, though, he amditted to seeing them several time.)

   Sometime, the legacy of Joy Division even crops up in the most unexpected places... it's not too fanciful to draw a parallel between Curtis' hyperactive trance dancing and the letting-it-all-out movements of rave culture, or between the pulverising rhythms of She's Lost Control and the industrial rock sound of, say, Nine Inch Nails. Where rave culture has been based upon exhilaration, however, Joy Division were about a cleansing, a purging of the soul. They came from repressed, turbulent times. Manchester in those days was a different place to the cafe bar and the shopping paradise we can all visit nowadays. The city was in turmoil, awash with unemployment, dilapidation and a socioeconomic disintigration that, for many, was symbolised when the city's sewage system collapsed in summer '79, filling the streets with an unremitting foul stench. This was the backdrop against which Joy Division - four deceptively ordinary, working class young men who saw something beyond the culture of no future - were working. The rest of it was a fateful collision of circumstances, accidents and coincidents. With the exception of drummer Stephen Morris' staccato rhythms, the band's members couldn't actually play, so they taught themselves. Peter Hook's revolutionary, mournful bass sound (and the use of the bass guitar as a lead instrument) came about partly from playing higher, louder notes in order to hear himself, and partly from his own uniquely complex character (brusque, no nonsense, but drawn to prolongued bouts of melancholia). Bernard Albrecht's skeletal, beautiful guitar playing came in direct response to the note-per-minute merchants of the day ("Isn't that terrible?" he once commented on Led Zeppelin), and out of a personality prone to reflection, insights and bouts of mischief. As for Ian Curtis, entire books have failed to thoroughly explain this bundle of paradoxes. How much of his worsening epilepsy and disintegrating personal circumstances informed his observations is a matter of conjecture... all we need really know is that he was a hugely gifted and insightful writer, perhaps one of the greatest of the 20th century, who just happened to be singing in a rock band.

   Live, Joy Division could be spellbinding, with people often leaving their gigs drenched in sweat and forever changed by the experience. One of those live performances - the band's two songs for BBC2's Something Else youth programme of September 1979 - is captured here, the band raging through Transmission and She's Lost Control as Ian Curtis allows himself a rare primal scream. When the programme was first broadcast, some viewers wrote in complaining that the entranced, dancing singer was on drugs. He wasn't. He was just giving himself over to the intensity that inevitably accompanied Joy Division's journey into the human psyche.

   After all these years, it's sometimes difficult to grasp how far they progressed musically in such a short space of time. But the two Peel sessions featured here - recorded a mere ten months apart - illustrate the qunatum leaps the band made in 1979. The first session, in January, captures Joy Division in the powerful build-up towards their Unknown Pleasures debut for Manchester's Factory Records. By the second, in November, there are hints - notably in the spectacularly eloquent Love Will Tear Us Apart - of the detached, eerie, serene (still) futuristic electronic sound subsequently unveiled on that single and the Closer album, sadly delivered after Curtis' death.

   These sessions capture not only the essence of the band - in their raw form, before the conjuror's hand of producer Martin Hannet - but offer an image of remarkable perfectionism. Soon after these recording, Curtis would further hone his lyrics (most notably transforming the Kakaesque Colony), and the band would quietly relegate the tensile Exercise One and colossal Sound Of Music in their set (alternative versions appeared on the posthumous collection, Still.). Excellent as these tracks are, we can only wonder at the processes by which the band deemed them not quite good enough for what they were striving for. Joy Division sought flawlessness, and achieved it, too.