Thanks so much for this really useful guide! I really enjoyed looking through it. 
You must have put a lot of effort into it.
I had no idea that M&S stock skincare products by Ren -- I haven't checked out their skincare/cosmetics section for some time. Or maybe it would just be in the larger London branches?
Chocolate-flavoured eyeshadow is a new one on me! (From your section on palettes). I think that being able to look at some of the available eyeshadow palettes all together like this is really useful. It's too easy to see them in a shop and buy them because the whole ensemble looks really pretty, then get your palette home and realise you already have most of the colours anyway, and the ones you didn't already have aren't that much use to you.
Heck, I'm old enough to remember when you could buy palettes like this on special offer in Harrods cosmetics hall for around a fiver! 
I did buy an eyeshadow palette by Accessorise a while back, though have hardly used it so far. I don't see Accessorise cosmetics getting much of a mention (not that I spend lots of time on beauty-related sites though). They seem fine, but do you know what kind of reputation they have? The number of cosmetic brands available these days is just staggering, compared with a couple of decades ago, don't you think?