So. Got a full fitting kit, same day, from RAE Autofactors in Roscrea. Only 10 euro, so couldn't be bothered rooting around the breakers.
Turned out it was actually one of the BOTTOM springs, the one that pulls the shoes against the threaded adjusters. Wtf!!???
I could have refitted the one that had somehow ended up caught at the top, but fired in a new one anyway.

Loose spring

Now, if any of you folk are stuck for any of the mounting bits for your BMW, you're welcome to what's in the picture.
All new apart from the dirty one. Which is fine tbh.
Mintex, not oem.

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