When both of my DSes were at secondary school they wore blazers, shirts and ties. We could source the blazers from John Lewis, M&S or a supermarket and sew the badges on. It was just as well really because in the final 2 years, DS2 went though 4 blazers due to a growth spurt.
The school decided to change that and you can only buy the blazers from them now. They are in the region of £40 each. The girls wear a regulation blouse and no tie, again only available from the school. The boys wear a tie.
Some of them look smart, some of them look like a bag of spanners. It doesn't matter if they have a blazer on if their shoes are scuffed and dirty, their trousers creased and their shirts crumpled.
I know at the DSes old school they weren't allowed to take off their blazers even on really hot days. They aren't, imo, the most comfortable piece of clothing either.
When they go to the sixth form they wear what they like. The lack of pockets hasn't caused them to lose money or phones, not wearing a blazer didn't make DS1's results go down or change his behaviour, and so far we are seeing the same with DS2.