"But I'm fairly sure that stick thin teenagers from the 1970s aren't shopping in Marks and Spencer."
I was a stick thin teenager in the 1970s and I can never find anything I like in M and S except for bras - and yes I used the MN measuring guide, but not being well endowed I find that they offer plenty of choice for my size.
I still go in optimistically just in case I see something I like. And occasionally I do find something, but generally I agree with the above comments.
I can't understand why they have got it so wrong. The basic principles of marketing are: listen to your customers and then try and anticipate your customers' needs, and they clearly aren't doing this.
Who are the people that make these woefully wrong decisions?