My co-ed Scottish school, both primary and secondary, did not require us to wear uniform, except on special occasions. Most of us did wear our royal blue blazers most of the time, and my mum expected us to wear the white shirt and school tie as well. Of course, we had gym slips for hockey- blue sashes for inter- school matches and house colours for inter-house games. I don't think big navy knickers were specified but we all wore them for PE. In the 1970-80s, my sons, in primary school, had no compulsory uniform, so it came as a shock when we had to invest in high school uniform, and again when we moved north.