It’s from M&S and I’ve managed to find a link for it although it’s no longer available.
www.marksandspencer.com/half-sleeve-waisted-midi-dress/p/clp60222351
I’m 5ft 7 and a dress size 10-12. This just sits really nicely and the ruched sleeves are really flattering. I also like the length as I like to wear my knee high heeled boots with dresses that cover the top of them.