‘Not v interesting” is Thom Yorke’s assessment of the 16-odd hours of unheard Radiohead music, recorded between 1995 and 1998, that the band have just shared online. Jonny Greenwood was marginally more effusive: “Only tangentially interesting. And very very long.” You get the sense that their hand was forced by a hacker who was hoping to charge $150,000 for the recordings, which were subsequently leaked; the band are now selling them and giving the proceeds to environmental campaigners Extinction Rebellion.

Yorke and Greenwood are absolutely wrong though. This is the holy grail – or perhaps Ark of the Covenant – for hardcore Radiohead disciples, and even has merit for less nerdish fans. It reveals the inner workings of what is regarded by many as the greatest album of the 1990s, showing how they walked alongside and then turned away from the brash Britpop that surrounded them. Here are some of the songs to look out for.

Lift (1:00:15 on MD126)

The nine versions of Lift across the MiniDiscs suggest this is the big song from this era that Radiohead could never get quite right. They did release a version of it eventually, for OK Computer’s 20th-anniversary edition – but it was much more muted than the ones they left in the vaults. Of the three studio versions here, #1 has the heavier guitars (9:46 on MD125), but #3 has the vocals mixed better, plus a nice keytar-ish solo. Either way, it’s the maximalist sound of peak Britpop: giant chords, even bigger string section, soaring Yorke top line. It’s what EMI were probably hoping for in a first single instead of Paranoid Android – and yet for all its satisfying robustness, along with the raptures among fans at this finally seeing the light, it is ultimately a conservative song and feels like a path the band were right to fork from. But a polished gem nevertheless.

True Love Waits (15:43 on MD111)

For years this was the great white whale for Radiohead fans – frequently played live, an acoustic version closed out their live album I Might Be Wrong before it was finally recorded, 20 years after it was written, in a twinkling, wintry, piano-driven version for A Moon Shaped Pool. Here we get the straightforward version many have craved. Driven by a characterful bassline – reminiscent of the one on Björk’s Come to Me – and an almost hip-hop breakbeat from Phil Selway, the rhythm section really suits it, though the meandering synth line is arguably distracting and underdone.

Attention (37:42 on MD115)

Or rather Attenzione! according to the Yorke-scrawled tracklisting. This song, a version of which got a super limited release on a cassette for OK Computer’s 20th anniversary, crops up a few times in various forms – this is the full-band version and therefore as definitive as it gets. It’s underpinned by remarkably breezy strummed chords, a little reminiscent of early songs like Stop Whispering where Yorke’s near-permanent shoulder tension seemed to relax. You can see why it was left off the fretful OK Computer, and suggests there was a much happier Britpop band that could have emerged out of The Bends.

“Hurts to Walk” (52:21 on MD112)

Another indication the band were making some much (fitter) happier material during the OK Computer sessions. Hurts to Walk – the fan title; judging from the MiniDisc label it could perhaps be called Girl Club or Get Together – ambles along with bright, cooing vocals behind its chorus, overstrummed guitar that has all the dopey warmth of a late-summer wasp. It sounds like Pavement fronted by a naive Brit, or the indie-slacker-Beach-Boys sound of Teenage Fanclub, who supported Radiohead on the OK Computer tour. A really endearing curio that suggests that once the band had vented their splenetic paranoia, it was all chill vibes, bro.

Last Flowers (2:42 on MD117)

With some different lyrics, this song eventually ended up on an In Rainbows bonus disc as a fairly typical Radiohead piano-and-acoustic trudge. The earlier version is more fleshed-out and idiosyncratic, with jaunty guitars, flirty lyrics (“Baby what you doing tonight?”) and a spiralling film-score synth line. The strings, done on synths in this demo version, suggest, as with Lift, that the band were quite taken with Britpop’s enthusiasm for string sections – most iconically on the Verve’s Bitter Sweet Symphony and Blur’s The Universal – but ultimately ditched them for a less obviously fashionable palette. A wise decision that has kept OK Computer isolated from its peers.

Unknown title (57:01 on MD113)

A peculiar jam that – truth be told – needs a lot more time in the oven. But it’s notable for the bright, crude synths, recalling Vangelis’s synthetic brass lines for the Blade Runner soundtrack, and there’s something seductive about its constant loping gait: it hints at the more purely electronic experiments that eventually ended up at Idioteque. This track comes off the back of what fans have called Thom’s Screechy Song, a pleasingly rough, ill-disciplined and noisy unreleased track with shades of Sonic Youth.

I Need a Job (22:10 on MD117)

There’s shades of 90s alt-rockers like Sebadoh to this choppy, strikingly straightforward tune – the kind of thing a conservative subset of Radiohead fans wish the band had continued to make instead of broadening out into OK Computer and Kid A. And to be fair, Yorke’s high, girlish voice does pair strongly with rather more knuckle-drugging guitars. Similar but not so good is MD115’s When I Get Bored Give Me One of Those, which, could easily have ended up as a bad Oasis imitation – but it equally could have been a National Anthem-sized experimental rocker.

Paranoid Android (5:36 on MD115)

Whole swathes of the MiniDiscs are given to alternate versions of OK Computer songs – or fragments, or live versions – which casual fans are unlikely to visit more than once. But this garage rock demo of Paranoid Android is great: rough and tumbling, it stretches to 11 minutes with a psych wig out at the end. The song’s weirdly liturgical extended middle eight is made even more holy with Yorke’s “hallelujahs”, which became wordless cries on the studio version.

Nude (49:54 on MD115)

The MiniDiscs aren’t short of scrappy Yorke solo takes, but these are at the very least always interesting – and in some cases startlingly beautiful. This waltzing version of Nude, Yorke’s voice reedy in the cheap microphone and the beat seemingly tapped out on a table, is testament to the strength of his songwriting. That lilting melody is instantly classic, even in such impoverished surroundings. At 9:05 on MD113, there’s a full-band version powered by organ; it would be another 10 years before it was finally recorded for In Rainbows in a much more delicate, grownup take.

A Reminder (0:00 on MD128)

Other Yorke solo numbers to check out include the ones that open MD118, particularly the detuned guitar instrumental at the very beginning – the kind of thing Alan Lomax might have recorded on a front porch in Mississippi. The most sublime, though, is this song, later fully recorded and included on the Airbag/How Am I Driving? EP in the wake of OK Computer. The a cappella demo is startlingly atmospheric. Recorded out on a hillside somewhere – you can hear someone tell Yorke “the whole mountain’s yours” before he begins singing – it’s just Yorke and the sound of the wind blowing across his microphone. The lyrics – “If I get old / I will not give in / But if I do / Remind me of this / Remind me that / Once I was free” – become intensely moving, an affirmation of the fire of life perched on the edge of the world.