Nailing a co-musician under a hotel room carpet after a hard night’s carousing. Playing spellbinding shows after intake of intoxicants that would send lesser mortals to A&E. The John Martyn story is made up of ample quantities of the unholy trinity – boozing, brawling and bad behaviour – that music media love to elevate to the level of a Legend.

This gigantic 18-disc set, containing well over 20 hours of music, and released to mark what would have been Martyn’s 65th birthday had he not passed away in January 2009 following years of ill health, proves that the music made by the singer-songwriter born as Ian McGeachy in 1948 is immeasurably more compelling than the age-old narrative of a musician squandering their talents in a hail of drink and drugs.

That Martyn isn’t better-known was down to choice, not lack of talent. Mercurial and perpetually shape-shifting, the picture painted by the dizzying, initially almost intimidating wealth of music contained here is that of an artist unwilling or unable to constrain their talent by the dictates of commercial considerations. The likes of Eric Clapton enjoyed hits with his tunes, but it’s near-impossible to imagine Martyn equipped with the kind of instantly recognisable ‘house style’ that enabled his unit-shifting admirers to become major stars: he was too busy innovating, pushing ever forwards. A man of contrasts and extremes, Martyn routinely followed delicate, tender performances with ribald comedy routines onstage, almost as if he was ashamed by the depth of feeling conjured by his best songs. He was also capable of moving seamlessly from sparse balladry to fearless bouts of intense inner-space exploration, armed only with his guitar and voice. Whilst such unpredictability pushed Martyn away from the mainstream for most of his musical journey, it’s kept his output fresh and surprising, ripe for discovery by those not yet bitten by the Martyn bug.

At his best (basically anything recorded between 1971 and 1980, a golden era when Martyn seemed incapable of putting a foot wrong), it’s not an exaggeration to describe Martyn as a genuine musical genius, seemingly unable to do the same thing twice or follow in anyone else’s tracks, routinely rendering familiar ingredients – a basic a guitar/voice singer-songwriter template – into compelling new shapes pulsating with fresh wonder. On the albums covered here, Martyn not only developed an instantly recognisable guitar style by experimenting with the time- and tone-bending Echoplex unit; he also moulded an entirely original singing style: a slurred, syllable-blending sweep that – at its best – turned his alternatingly tender and roaring vocals into a human equivalent of a soaring saxophone. Such dazzling talents were married to an immense songwriting gift: Martyn certainly wasn’t messing with his vocals to disguise any shortcomings in the lyrics or melody department.

The Island Years, however, goes for a more complete, complex and honest picture than what would be provided by simply celebrating Martyn’s proudest achievements. Both the early works where Martyn was finding his feet and his 80′s return to Island Records as a slick MOR balladeer are covered in full. All the studio albums released by Island are here, backed by a near-boundless (if you’re burdened by any sort of everyday responsibilities, it will take you weeks to plough through this set) selection of outtakes, alternative versions, live takes and rarities, ranging from revelatory (incredible live cuts from the 80′s, when Martyn was meant to be past it) to the for-obsessives-only (alternative versions virtually identical to what ended up on the album) and amusing oddities (a 1980 cover of Tommy Tucker’s rhythm & blues classic ‘Hi Heel Sneakers’, apparently the first record Martyn bought).

Little in the early albums indicates the arrival of a major talent. There’s nothing wrong with London Conversation (1967) or The Tumbler (1968) as such, but the period trappings – sitar ragas on ‘Rolling Home’, a Bob Dylan cover (‘Don’t Think Twice It’s Alright’), the slightly over-chirpy fairy tale whimsy of ‘Sing a Song of Summer’ – tie them tightly into the times they were made in. Recorded as a duo with wife Beverley, Stormbringer and Road to Ruin (both 1970) are much more compelling: made in Woodstock with members of The Band, the best bits of the former count amongst the funkiest things Martyn ever made. However, the strings and piano on the majestic title track – a forgotten masterpiece – nod deep towards Island label mate Nick Drake. It would be a long, long time before Martyn sounded remotely like anyone else again.