I go into M&S because I love Nuxe, and I sometimes go into the food hall whilst I'm there.
Clothes? Not for ages. The last time I did was in the 1980s, when you could reliably buy serviceable, fairly classic, durable clothes, usually in natural fibre and made in Britain. So you could get lots of workwear and staples, and feel good about the British economy too.
Then Sloane Rangerdom came along and suddenly they were fashionable and it went to their heads. It's just never been the same since.
They need to decide who their target market is, and then do it really well. I get no sense whatsoever of what sort of person would buy clothes from there.
(For plain bras in bright colours btw, try ASDA. They do a basic Tshirt bra (moulded cup) and always seem to have it in stock in white, black and nude, plus a regularly changed range of colours).