@AC - Documents? What documents?
"How could these documents have existed in the first place given her cleaner had no right to work in the UK? How could she have actually examined documents that didn't exist?"
The rules regarding keeping photocopies of documents is there to deal with this very issue. If the employer has a photocopy of a legitimate looking document then they are absolved of all blame. If they don't have the photocopy then the assumption is made that they didn't check. The problem being that there are an awful lot of forged documents about, or at least legit documents which have been doctored (dates altered and the likes).
If an employer has a photocopy of a legit looking, but dodgy document they have proof that they have been conned. And therein lies the problem. There are employers out there who are providing illegals with fake docs in order that they can employ them, but this ruling gives them a simple loophole.
I suppose the lack of a copy sort of proves that Scotland is only slightly dodgy, not totally bent.