Although the debate on the effect of uniform in schools is a valid one, I think in this discussion it should be accepted for the minute that within the British school system uniform, for the moment, is regarded as important and that ranting against the "stupidity" of it is not going to solve anything. Especially when most parents when consulted by the school state that they prefer uniform to non-uniform.
Schools are placed in a very difficult position of having to meet the needs and wants of a range of stakeholders. Parents, students, teachers, Govenors, OFSTED, the Government and the community within which they operate. This is fantastically difficult job and although some stakeholder interests are closely linked and therefore a higher than others, all must be appeased.
The difficulty when it comes to uniform and appearance is in the interest of many of the that the interests of many of the stakeholders of a school that the public perception of the school is good. Parents, Governors, Teachers and pupils (it can have an effect when applying for jobs in the local area!) all have an strong vested interest in this. For example as the number of students on roll has an effect on the amount of funding a school gets, and thus how well they can provide an education to the students, a public perception that the school is a good with a constructive and disciplined environment for learning effects how many students attend.
As one of the things that effects this perception is the presentation of the students then uniform and the way it is worn becomes an issue. Dismissing this because of your own opinion is very dangerous, as you are just one of many who have a stake in the school.
I'll take the make up issue for one, most schools are stuck between banning make up and allowing it. Very good points made on here about a total ban meaning that self conscious girls with acne are going to feel uncomfortable. But schools are also stuck in the position that allowing make up can mean girls coming to school wearing a full face of make up that has taken an age to put on (which can cause parents difficulties in the morning) and the distraction of the constant need to be topping it up being a distraction from their work in lesson. So the schools tend to opt with "subtle" or "discreet" make up, of which lets be honest a bright shade of red is not.
Once a uniform has been set, and rules agreed it is down to the staff to implement them, some staff will choose not to implement the rules all the time, but many will. One of the reasons that many staff do adhere to the rules set by the school all the time is that it creates a standard approach, if everyone goes by the same rules there is no room for deflective behaviour when dealing with students. Cries of "Well Miss Smith lets me" "Or look at such and such" are not helpful when enforcing school policy no matter what the indiscretion is.
There have been some bad examples of implementation of rules on here, and in the schools I have worked in (and I've been in the profession longer than I would like to remind myself about, it makes me feel very old) I have rarely seen discipline that badly managed, I would definitely say that the school refusing to let students leave even if the detention is set on the day are on a sticky wicket if they were ever properly challenged.
Their may be many reasons for rules on hair or whatever matter of a students appearance but schools make decisions based on the needs of the entire community, not just individuals.
The comments about "rigid adherence" to rules have been dismissed above but those on teacher's fragile egos are and ad hominem attack and therefore they invalidate the argument. Also many posters have said teachers don't make the rules, they enforce them, and many, many school push uniform hard, so teachers are stuck between being told that they are not doing their job by management and having some leeway. In reality all schools give students who have specific needs, even with uniform, a bit of leeway, but most follow the rules.
Lord and the Ilk who cry "my child will not" and shout about their rights have very little understanding of how the system actually works. If Lord think he can circumvent the school rules and quote human rights at his child's school he is welcome to try, but unless there is a legitimate breach of them, his cries will fall on deaf ears. The child has a right to education, but the parent and child do not have a right to disrupt others learning, or to only operate within the school community on their own terms. Lord will have about as much chance of doing the things he says he will as those who claim to be "freemen on the land" do in court.
The sexulisation of girls, and discrimination against girls where uniform is concerened, is an issue, but it is a societal issue that will take decades of hard work to change, but yet is another thing thrown on to the pile that schools are asked to address on top of providing education. Until we as parents, family and a society stop praising little girls for being pretty, and stop judging older females on their appearance, splashing it over magazines etc girls will take the message that their appearance is vitally important, and they will then take that as one of the ways in which they are valued. You cannot expect schools to be the only theater of social change or ask them to accept responsibility for it.
So either we go for a massive societal change in the way the British education system works, the way that we raise and talk to our daughters and behave towards other women. Or we settle to adhere to rules that for the most meet the needs of the whole school community.
Or you can just launch attacks on teachers here, I know which one will happen.