I don't think anybody should buy electrical products from a company whose level of expertise is such that they think this is a schematic showing how their product is wired:
hah, very interesting photos here! Thanks for all the comments.
What I did in the end was a rather over-engineered solution, and unnecessary considering that all the cables came to a central point. But, it gives my friend confidence regarding the layout and it didn't really take much longer than sticking everything into one box. Basically I split it all up into four new junction boxes (the 65p-from-screwfix sort), one for each of the four lights+switches being served, with just very short cable between each box, and mounted them all on some board which I then mounted low on the back wall of the attic.
(I also added a fifth junction box to serve the new attic lights which was the whole purpose of my original investigation)
I think the main attraction of loop-in wiring is that all the connections remain accessible (at rose and/or switch) even if there is no access to the space above the ceiling. However, the technique is (in my opinion) not without its downsides.
My usual method of wiring upstairs lights through the loft was to bring all the cables back to the hatch and use a J701 fixed to a purlin or similar and connect up stood on the ladder, it to has its downsides
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