Available in a dizzying array of formats, it’s likely that what’s being marketed as Achtung Baby’s “uber deluxe” version of 10 discs (six CDs, four DVDs) will only be snapped up by diehard fans with the deepest pockets - it’s listed on Amazon for a whopping £268.

That’s a pity, as although the unreleased “new” songs previewed in this article are available on a more affordable two-disc standard deluxe release, the embryonic “Kindergarten” versions are restricted to the more elaborate packages.

These are the familiar songs in fledgling form, which, more than anything else on offer, chart the step-by-step progress of a band searching for a new sound, striving for reinvention and reinvigoration.

Nonetheless, Achtung Baby remains arguably U2’s most remarkable album; perhaps not as lauded as the world-conquering Joshua Tree, but an intriguing illustration of a band heading back to the drawing board after the success of that earlier record had, to all intents and purposes, painted them into a creative corner.

The 20th anniversary edition of Achtung Baby, in its many formats, is released through Universal/Island on 31 October