Radiohead on BBC Radio 4

The sleeves came out of hundreds of sketches in many different materials, most of them never seen. Thom Yorke says the work got lost because it did not make sense at the time, and putting it together now was a way of making sense of it after the fact.

Going back through it, Stanley Donwood says, was like looking at the work of a badly designed clone of himself, recognisably the same but everything a little shaky and not very well drawn. He found reconnecting with it unsettling.

At the time they did not know where to go next and did not want to make another guitar record. The success of the previous album bought them an absence of deadlines, which they spent trying to turn record packaging into fine art.

The virtual exhibition started as a walkthrough of a gallery and grew more interesting once they realised the software let them break every physical rule. They describe a forest built from the sketchbooks, a vortex, and a pyramid full of praying creatures, which Yorke compares to a circular hell out of Flann O'Brien.