Piglet you said "if it's something going on within the family (which it most often is)". The context was any discussion about sex, relationships or being pregnant (which is what I originally said parents should be informed of with an exception if the teacher believed they were at risk)
I am aware that most child abuse is perpetrated in the family. Math that's like saying that "raising taxes on millionaires to 75% isn't an anti-wealth position, just a pro-equality position." Even if it's pro-equality it still goes against someone (i.e. the wealthy.)
Telling parents that their children will be able to explore their sexual concerns with professionals at school and they have no way of finding out any information is "anti-parent" AND "pro-confidentiality". It depends whether you believe parents' right to know or the young person's right to privacy is more important. There is no law or absolute rule either way in this country, so schools have discretion without getting into trouble for which way they decide.
If it's a place in Islington or the leafy suburbs of Cambridge where 97% of parents would prefer their DCs had an outside "confidante" it makes sense to not inform them. If it's inner city with majority Muslims or Black Charismatics or anyone else who would want to know if their DC was up to something they considered to be very immoral, better to inform parents.
Still does not require rejecting the "primacy of Western values" you mentioned or ignoring beatings at madrassahs, pupils coming in full of bruises which their parents believe are "justified discipline", FGM, Kindoki, violent "exorcism", forced marriage or other such practices which violate their individual rights as children, British citizens and more than anything as human beings.
Am I not promoting an even-handed moderate position here? The anti-extremist as ever...