Kind of non uniform in primary school (early 1980s)- there was a school T shirt, school colours of grey and maroon and blue, and even a school tie but it was all entirely optional - many of us wore some form of uniform eg a gingham dress, or a blouse and skirt, but equally, looking at the class pics, many were wearing colourful T shirts, tracksuits, dresses, football shirts...For some reason I never questioned why I was in a grey skirt and blouse and my friend was wearing a polka dot summer dress.
Secondary school (girls school) was uniform, but it was quite lax - no tie, a blazer existed but very few wore it, we could get away with quite a lot in terms of length and style of skirt - every so often there was a clamp down but there were girls wearing loose denim shirts instead of the formal ones, and DMs.
Sixth form at the school = no uniform, I believe now they have to wear "business wear" whatever that is but our rules were "no beachwear, no halter necks" -anything else fine! In practice most people wore jeans and T-shirts.