It is a nice dress and I am not an M&S fan of late, possibly with the exception of lingerie.
The OP has resolved this now, l hope she managed to take it off again!
I would certainly post a review with an adverse comment.
Historically, the more expensive garments did up at the back because “refined ladies 😂” were expected th have a dresser or a maid to assist them. That was after they had been eased into their corset!
Oh, for the front zip! Which can look very stylish.