Aw, that's lovely! I honestly didn't know grammar schools (& the minor public schools who gave free "grammar school" places, like the GPDST which is where I went), had more uniform than, say, the comprehensives. Everyone seemed to wear school uniform in those days, including ugly regulation indoor and outdoor shoes, stupid hats which had to be worn, heavy gaberdine raincoats and all the rest. I suppose the initial outlay was expensive, after that it was just a question of replacing things as they were outgrown or worn out. The only thing I liked was the scarf for some reason, I hung onto mine years after I was expelled, and the blazer wasn't bad.
The thing about regulation school uniforms is that there is no competition during the school week, parents don't have to supply endless outfits and shoes, especially for girls, and in my day clothes were a lot more expensive than now.
The local comp girls had to wear similar to us.
School uniforms are far more sensible and comfortable now, thank goodness.