I'm sure this has become worse. It seems to have happened with the change in many places to "academy" schools, where appearance reigns and they're run like businesses.

In the 1990s-2000s, when my parents were both teachers and I was at school, "uniform" meant wearing the correct colours (e.g. dark trousers or skirt, white shirt/t-shirt, blue jumper/sweater). It was still ridiculous, but being punished for it would require repeatedly breaking those rules. The usual response was the teacher saying "tuck your shirt in, William".